[runtimes][cmake] Propagate cmake arguments.

[Mordante]

Summary

The documentation [1] has an example

$ cmake -G Ninja -S runtimes -B build \

-DLLVM_ENABLE_RUNTIMES="libcxx"           \
-DLIBCXX_CXX_ABI=libstdc++                \
-DLIBCXX_CXX_ABI_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"

Unfortunately the LIBCXX_ cmake arguments aren't forwarded to the CMake
for libc++. This was discovered while working on enabling modules in the
libc++ bootstrap CI build.

[1] https://libcxx.llvm.org/BuildingLibcxx.html#using-libsupc-on-linux

Depends on D158860

[ldionne]

@phosek Didn't we already support passing e.g. LIBCXX_ENABLE_FOO variables through the bootstrapping build? I can't find where that's done though.

[phosek]

In D158878#4639752, @ldionne wrote:

@phosek Didn't we already support passing e.g. LIBCXX_ENABLE_FOO variables through the bootstrapping build? I can't find where that's done though.

We do for the default target, see my comment. @Mordante Can you share the full CMake invocation?

llvm/runtimes/CMakeLists.txt

353

This code path is only used with LLVM_RUNTIME_TARGETS, passing through all variables into every target is a breaking change because not all variables might be applicable to every target.

398

We already passthrough prefixes into the default target here.

[Mordante]

llvm/runtimes/CMakeLists.txt

398

I tried this the the option -DLIBCXX_ENABLE_STD_MODULES=ON in D158934. Should that patch work "out-of-the-box"? If so I can retest that patch without this one.

[phosek]

llvm/runtimes/CMakeLists.txt

398

It should, let me know if it doesn't work and I can take a look.

llvm/runtimes/CMakeLists.txt

 # TODO: This file assumes the Clang toolchain so it'd be better if it lived in
 # Clang, except there already is clang/runtime directory which contains
 # similar although simpler functionality. We should figure out how to merge
 # the two files.
 
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON")
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   set(proj_dir "${CMAKE_CURRENT_SOURCE_DIR}/../../${proj}")
   if(IS_DIRECTORY ${proj_dir} AND EXISTS ${proj_dir}/CMakeLists.txt)
     list(APPEND runtimes ${proj_dir})
   else()
     message(FATAL_ERROR "LLVM_ENABLE_RUNTIMES requests ${proj} but directory not found: ${proj_dir}")
   endif()
   string(TOUPPER "${proj}" canon_name)
   STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
+  list(APPEND RUNTIMES_CMAKE_PREFIXES "${canon_name}_")
   set(LLVM_EXTERNAL_${canon_name}_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../../${proj}")
 endforeach()
 
 function(get_compiler_rt_path path)
   foreach(entry ${runtimes})
     get_filename_component(projName ${entry} NAME)
     if("${projName}" MATCHES "compiler-rt")
       set(${path} ${entry} PARENT_SCOPE)
llvm_ExternalProject_Add(runtimes-${name}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
                                       -DLLVM_RUNTIMES_TARGET=${name}
                                       ${COMMON_CMAKE_ARGS}
                                       ${${name}_extra_args}
+                           PASSTHROUGH_PREFIXES ${RUNTIMES_CMAKE_PREFIXES}
                            EXTRA_TARGETS ${${name}_extra_targets}
                                          ${${name}_test_targets}
                            USE_TOOLCHAIN
                            ${EXTRA_ARGS} ${ARG_EXTRA_ARGS})
 endfunction()
 
 if(runtimes)
   # Create a runtimes target that uses this file as its top-level CMake file.
if(LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
         endif()
       endforeach()
     endif()
   endif()
   if(NOT LLVM_RUNTIME_TARGETS)
     runtime_default_target(
       DEPENDS ${builtins_dep} ${extra_deps}
       CMAKE_ARGS ${libc_cmake_args}
       PREFIXES ${prefixes})
     set(test_targets check-runtimes)
   else()
     if("default" IN_LIST LLVM_RUNTIME_TARGETS)
       runtime_default_target(
         DEPENDS ${builtins_dep} ${extra_deps}
         CMAKE_ARGS ${libc_cmake_args}
         PREFIXES ${prefixes})
       list(REMOVE_ITEM LLVM_RUNTIME_TARGETS "default")