[libc++] Default to vcruntime when targeting MSVC

[smeenai]

Summary

libc++abi is never the right option for LIBCXX_TARGETING_MSVC, since it
targets the Itanium ABI, whereas MSVC uses the Microsoft ABI. Make the
default ABI be vcruntime when targeting MSVC even if libc++abi is
present in the tree.

[EricWF]

LGTM.

CMakeLists.txt

119 ↗

(On Diff #96042)

Nit: I would rather see this be

elseif ((NOT LIBCXX_STANDALONE_BUILD OR HAVE_LIBCXXABI) AND
        IS_DIRECTORY "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")

That way we can avoid a level of nesting.

[smeenai]

CMakeLists.txt

119 ↗

(On Diff #96042)

Sounds good; will change before committing.

[smeenai]

Reduce nesting (address comments)

libcxx/trunk/CMakeLists.txt

 if (LIBCXX_CXX_ABI STREQUAL "default")
   find_path(
     LIBCXX_LIBCXXABI_INCLUDES_INTERNAL
     cxxabi.h
     PATHS ${LLVM_MAIN_SRC_DIR}/projects/libcxxabi/include
           ${LLVM_MAIN_SRC_DIR}/runtimes/libcxxabi/include
     NO_DEFAULT_PATH
   )
-  if ((NOT LIBCXX_STANDALONE_BUILD OR HAVE_LIBCXXABI) AND
+  if (LIBCXX_TARGETING_MSVC)
+    # FIXME: Figure out how to configure the ABI library on Windows.
+    set(LIBCXX_CXX_ABI_LIBNAME "vcruntime")
+  elseif ((NOT LIBCXX_STANDALONE_BUILD OR HAVE_LIBCXXABI) AND
           IS_DIRECTORY "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
     set(LIBCXX_CXX_ABI_LIBNAME "libcxxabi")
     set(LIBCXX_CXX_ABI_INCLUDE_PATHS "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
     set(LIBCXX_CXX_ABI_INTREE 1)
-  else()
-    if (LIBCXX_TARGETING_MSVC)
-      # FIXME: Figure out how to configure the ABI library on Windows.
-      set(LIBCXX_CXX_ABI_LIBNAME "vcruntime")
-    elseif(APPLE)
-      set(LIBCXX_CXX_ABI_LIBNAME "libcxxabi")
-      set(LIBCXX_CXX_ABI_SYSTEM 1)
-    else()
-      set(LIBCXX_CXX_ABI_LIBNAME "default")
-    endif()
-  endif()
+  elseif (APPLE)
 else()
   set(LIBCXX_CXX_ABI_LIBNAME "${LIBCXX_CXX_ABI}")
 endif()
 
 # Use a static copy of the ABI library when linking libc++. This option
 # cannot be used with LIBCXX_ENABLE_ABI_LINKER_SCRIPT.
 option(LIBCXX_ENABLE_STATIC_ABI_LIBRARY "Statically link the ABI library" OFF)