[libc++] Refactor the Apple build scripts

[ldionne]

Summary

This patch upstreams some changes we've made internally to how we're
building the libc++ dylib on Apple platforms. The goal is still to
eventually get rid of apple-install-libcxx.sh entirely and have a
proper way to mirror what we do internally with just the normal CMake
configuration.

[ldionne]

Fix CI.

[ldionne]

Try to fix CI again -- this should work since we're overriding the backdeployment config explicitly.

[ldionne]

Rebase onto main -- that should fix the CI.

libcxx/cmake/caches/Apple.cmake

 set(LIBCXX_ENABLE_INCOMPLETE_FEATURES OFF CACHE BOOL "")
 
 set(LIBCXX_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
 set(LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
 
 set(LIBCXXABI_ENABLE_ASSERTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_FORGIVING_DYNAMIC_CAST ON CACHE BOOL "")
 
+set(LIBCXX_TEST_CONFIG "apple-libc++-shared.cfg.in" CACHE STRING "")
+set(LIBCXXABI_TEST_CONFIG "apple-libc++abi-shared.cfg.in" CACHE STRING "")
 set(LIBCXX_TEST_PARAMS "stdlib=apple-libc++" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")

libcxx/utils/ci/apple-install-libcxx.sh

 
 --build-dir <DIR>            Path to the directory to use for building. This will
                              contain intermediate build products.
 
 --install-dir <DIR>          Path to the directory to install the library to.
 
 --symbols-dir <DIR>          Path to the directory to install the .dSYM bundle to.
 
---sdk <SDK>                  SDK used for building the library. This represents
-                             the target platform that the library will run on.
-                             You can get a list of SDKs with \`xcodebuild -showsdks\`.
-
 --architectures "<arch>..."  A whitespace separated list of architectures to build for.
                              The library will be built for each architecture independently,
                              and a universal binary containing all architectures will be
                              created from that.
 
+--headers-only               Only install the header part of the library -- don't actually
+                             build the full library.
+
 --version X[.Y[.Z]]          The version of the library to encode in the dylib.
 EOF
 }
 
 while [[ $# -gt 0 ]]; do
     case ${1} in
         -h|--help)
             usage
case ${1} in
         --symbols-dir)
             symbols_dir="${2}"
             shift; shift
             ;;
         --install-dir)
             install_dir="${2}"
             shift; shift
             ;;
-        --sdk)
-            sdk="${2}"
-            shift; shift
-            ;;
         --architectures)
             architectures="${2}"
             shift; shift
             ;;
+        --headers-only)
+            headers_only=true
+            shift
+            ;;
         --version)
             version="${2}"
             shift; shift
             ;;
         *)
             error "Unknown argument '${1}'"
             ;;
     esac
 done
 
-for arg in llvm_root build_dir symbols_dir install_dir sdk architectures version; do
+for arg in llvm_root build_dir symbols_dir install_dir architectures version; do
     if [ -z ${!arg+x} ]; then
         error "Missing required argument '--${arg//_/-}'"
     elif [ "${!arg}" == "" ]; then
         error "Argument to --${arg//_/-} must not be empty"
     fi
 done
 
 # Allow using relative paths
function step() {
     echo "${separator}"
     echo "${1}"
     echo "${separator}"
 }
 
 for arch in ${architectures}; do
     step "Building libc++.dylib and libc++abi.dylib for architecture ${arch}"
     mkdir -p "${build_dir}/${arch}"
-    (cd "${build_dir}/${arch}" &&
-        xcrun --sdk "${sdk}" cmake "${llvm_root}/runtimes" \
+    xcrun cmake -S "${llvm_root}/runtimes" \
+                -B "${build_dir}/${arch}" \
                 -GNinja \
-            -DCMAKE_MAKE_PROGRAM="$(xcrun --sdk "${sdk}" --find ninja)" \
-            -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+                -DCMAKE_MAKE_PROGRAM="$(xcrun --find ninja)" \
                 -C "${llvm_root}/libcxx/cmake/caches/Apple.cmake" \
+                -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
                 -DCMAKE_INSTALL_PREFIX="${build_dir}/${arch}-install" \
                 -DCMAKE_INSTALL_NAME_DIR="/usr/lib" \
                 -DCMAKE_OSX_ARCHITECTURES="${arch}" \
-            -DLIBCXXABI_LIBRARY_VERSION="${version}" \
-            -DLIBCXX_INCLUDE_BENCHMARKS=OFF \
-            -DLIBCXX_TEST_CONFIG="apple-libc++-shared.cfg.in" \
-            -DLIBCXXABI_TEST_CONFIG="apple-libc++abi-shared.cfg.in"
-    )
+                -DLIBCXXABI_LIBRARY_VERSION="${version}"
 
-    xcrun --sdk "${sdk}" cmake --build "${build_dir}/${arch}" --target install-cxx install-cxxabi -- -v
+    if [ "$headers_only" = true ]; then
+        xcrun cmake --build "${build_dir}/${arch}" --target install-cxx-headers -- -v
+    else
+        xcrun cmake --build "${build_dir}/${arch}" --target install-cxx install-cxxabi -- -v
+    fi
 done
 
 function universal_dylib() {
     dylib=${1}
 
     inputs=$(for arch in ${architectures}; do echo "${build_dir}/${arch}-install/lib/${dylib}"; done)
 
     step "Creating a universal dylib ${dylib} from the dylibs for all architectures"
-    xcrun --sdk "${sdk}" lipo -create ${inputs} -output "${build_dir}/${dylib}"
+    xcrun lipo -create ${inputs} -output "${build_dir}/${dylib}"
 
     step "Installing the (stripped) universal dylib to ${install_dir}/usr/lib"
     mkdir -p "${install_dir}/usr/lib"
     cp "${build_dir}/${dylib}" "${install_dir}/usr/lib/${dylib}"
-    xcrun --sdk "${sdk}" strip -S "${install_dir}/usr/lib/${dylib}"
+    xcrun strip -S "${install_dir}/usr/lib/${dylib}"
 
     step "Installing the unstripped dylib and the dSYM bundle to ${symbols_dir}"
-    xcrun --sdk "${sdk}" dsymutil "${build_dir}/${dylib}" -o "${symbols_dir}/${dylib}.dSYM"
+    xcrun dsymutil "${build_dir}/${dylib}" -o "${symbols_dir}/${dylib}.dSYM"
     cp "${build_dir}/${dylib}" "${symbols_dir}/${dylib}"
 }
 
+if [ "$headers_only" != true ]; then
     universal_dylib libc++.1.dylib
     universal_dylib libc++abi.dylib
     (cd "${install_dir}/usr/lib" && ln -s "libc++.1.dylib" libc++.dylib)
+fi
 
 # Install the headers by copying the headers from one of the built architectures
 # into the install directory. Headers from all architectures should be the same.
 step "Installing the libc++ and libc++abi headers to ${install_dir}/usr/include"
 any_arch=$(echo ${architectures} | cut -d ' ' -f 1)
 mkdir -p "${install_dir}/usr/include"
 ditto "${build_dir}/${any_arch}-install/include" "${install_dir}/usr/include"
 ditto "${llvm_root}/libcxxabi/include" "${install_dir}/usr/include" # TODO: libcxxabi should install its headers in CMake
 if [[ $EUID -eq 0 ]]; then # Only chown if we're running as root
     chown -R root:wheel "${install_dir}/usr/include"
 fi
 
+if [ "$headers_only" != true ]; then
     step "Installing the libc++ and libc++abi licenses"
     mkdir -p "${install_dir}/usr/local/OpenSourceLicenses"
     cp "${llvm_root}/libcxx/LICENSE.TXT" "${install_dir}/usr/local/OpenSourceLicenses/libcxx.txt"
     cp "${llvm_root}/libcxxabi/LICENSE.TXT" "${install_dir}/usr/local/OpenSourceLicenses/libcxxabi.txt"
 
     # Also install universal static archives for libc++ and libc++abi
     libcxx_archives=$(for arch in ${architectures}; do echo "${build_dir}/${arch}-install/lib/libc++.a"; done)
     libcxxabi_archives=$(for arch in ${architectures}; do echo "${build_dir}/${arch}-install/lib/libc++abi.a"; done)
     step "Creating universal static archives for libc++ and libc++abi from the static archives for each architecture"
     mkdir -p "${install_dir}/usr/local/lib/libcxx"
-xcrun --sdk "${sdk}" libtool -static ${libcxx_archives} -o "${install_dir}/usr/local/lib/libcxx/libc++-static.a"
-xcrun --sdk "${sdk}" libtool -static ${libcxxabi_archives} -o "${install_dir}/usr/local/lib/libcxx/libc++abi-static.a"
+    xcrun libtool -static ${libcxx_archives} -o "${install_dir}/usr/local/lib/libcxx/libc++-static.a"
+    xcrun libtool -static ${libcxxabi_archives} -o "${install_dir}/usr/local/lib/libcxx/libc++abi-static.a"
+fi

libcxx/utils/ci/run-buildbot

generic-abi-unstable)
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-abi-unstable.cmake" \
                    -DLIBCXX_TEST_CONFIG="llvm-libc++-shared.cfg.in" \
                    -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in"
     check-runtimes
 ;;
 apple-system)
     clean
 
-    sdk_root="$(xcrun --sdk macosx --show-sdk-path)"
     arch="$(uname -m)"
-
+    xcrun --sdk macosx                                              \
         ${MONOREPO_ROOT}/libcxx/utils/ci/apple-install-libcxx.sh    \
             --llvm-root ${MONOREPO_ROOT}                            \
             --build-dir ${BUILD_DIR}                                \
             --install-dir ${INSTALL_DIR}                            \
             --symbols-dir "${BUILD_DIR}/symbols"                    \
-        --sdk "macosx"                                          \
             --architectures "${arch}"                               \
             --version "999.99"
 
     # TODO: It would be better to run the tests against the fake-installed version of libc++ instead
     xcrun --sdk macosx ninja -vC "${BUILD_DIR}/${arch}" check-cxx check-cxxabi
 ;;
 apple-system-backdeployment-*)
     clean
 
     if [[ "${OSX_ROOTS}" == "" ]]; then