[CMake][AIX] Set LLVM_ENABLE_PER_TARGET_RUNTIME_DIR appropriately for AIX

[daltenty]

Summary

AIX by default usually folds 32-bit & 64-bit arch libraries into a single
archive, a behaviour we may want for the runtime libraries in the future,
so we don't necessarily want to opt into the multlib layout introduce in
D45604, which is currently the default for runtime builds.

[hubert.reinterpretcast]

llvm/runtimes/CMakeLists.txt

263

Should there be a comment on this block too?

409

s/folds/should fold/;
I would suggest to move the comment to just before the AIX block.

[daltenty]

• Adjust comments

[hubert.reinterpretcast]

LGTM; thanks.

llvm/runtimes/CMakeLists.txt

${error} Set RUNTIMES_BUILD_ALLOW_DARWIN to allow a single darwin triple.")
         message(FATAL_ERROR "${error}")
       endif()
     endforeach()
   endfunction()
 
   function(builtin_default_target compiler_rt_path)
     cmake_parse_arguments(ARG "" "" "DEPENDS" ${ARGN})
 
+    set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default ON)
+    # AIX should fold 32-bit & 64-bit arch libraries into a single archive.
+    if (TARGET_TRIPLE MATCHES "aix")
+      set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)
+    endif()
+
     llvm_ExternalProject_Add(builtins
                              ${compiler_rt_path}/lib/builtins
                              DEPENDS ${ARG_DEPENDS}
                              CMAKE_ARGS -DLLVM_LIBRARY_OUTPUT_INTDIR=${LLVM_LIBRARY_DIR}
                                         -DLLVM_RUNTIME_OUTPUT_INTDIR=${LLVM_TOOLS_BINARY_DIR}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_TRIPLE}
-                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
+                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default}
                                         -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_ASM_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_C_COMPILER_WORKS=ON
                                         -DCMAKE_ASM_COMPILER_WORKS=ON
                                         ${BUILTINS_CMAKE_ARGS}
                              PASSTHROUGH_PREFIXES COMPILER_RT
                              USE_TOOLCHAIN
                              ${EXTRA_ARGS})
foreach(component ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
         list(APPEND extra_targets ${component} install-${component} install-${component}-stripped)
       endif()
     endforeach()
 
     if(LLVM_INCLUDE_TESTS)
       list(APPEND test_targets runtimes-test-depends check-runtimes)
     endif()
 
+    set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default ON)
+    # AIX should fold 32-bit & 64-bit arch libraries into a single archive.
+    if (TARGET_TRIPLE MATCHES "aix")
+      set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)
+    endif()
+
     llvm_ExternalProject_Add(runtimes
                              ${CMAKE_CURRENT_SOURCE_DIR}
                              DEPENDS ${ARG_DEPENDS} ${CXX_HEADER_TARGET}
                              # Builtins were built separately above
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_TRIPLE}
                                         -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
-                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
+                                        -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default}
                                         -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_CXX_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_ASM_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_C_COMPILER_WORKS=ON
                                         -DCMAKE_CXX_COMPILER_WORKS=ON
                                         -DCMAKE_ASM_COMPILER_WORKS=ON
                                         ${RUNTIMES_CMAKE_ARGS}
                              PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES