[libc][CMake] Place archives in build/lib/<target-triple>

[aidengrossman]

Summary

This patch moves the location of libllvmlibc.a within the build tree to
within ./lib/<target triple>. This more closely matches the behavior of
other runtime builds and allows for clang in the same build tree to
automatically be able to link against llvmlibc since this path is by
default included by the driver.

Also removes the LIBC_BINARY_DIR CMake flag since it isn't used anywhere
in the tree (based on a quick grep).

[aidengrossman]

This will be necessary for using https://reviews.llvm.org/D151013 in multi-stage builds automatically. This is the default behavior of the libcxx builds (logic was copied from there), which can be automatically linked against in multi-stage builds since clang by default includes this directory. I wasn't able to find any specific reason the LLVM libc static archives were placed where they were, but it's very possible I could be missing something there.

[phosek]

LGTM

libc/cmake/modules/LLVMLibCLibraryRules.cmake

138

I think we should use ${LIBC_LIBRARY_DIR} here as well.

libc/CMakeLists.txt

 cmake_minimum_required(VERSION 3.20.0)
 
 # Include LLVM's cmake policies.
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
 # Default to C++17
 set(CMAKE_CXX_STANDARD 17)
 
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
 
-# The top-level sourse and binary directories.
+# The top-level source directory.
 set(LIBC_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
-set(LIBC_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 # The top-level directory in which libc is being built.
 set(LIBC_BUILD_DIR ${CMAKE_CURRENT_BINARY_DIR})
 
+if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR)
+  set(LIBC_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE})
+else()
+  if(LLVM_LIBRARY_OUTPUT_INTDIR)
+    set(LIBC_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
+  else()
+    set(LIBC_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX})
+  endif()
+endif()
+
 if(LLVM_LIBC_FULL_BUILD OR LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
   if(NOT LIBC_HDRGEN_EXE)
     # We need to set up hdrgen first since other targets depend on it.
     add_subdirectory(utils/LibcTableGenUtil)
     add_subdirectory(utils/HdrGen)
   else()
     message(STATUS "Will use ${LIBC_HDRGEN_EXE} for libc header generation.")
   endif()

libc/cmake/modules/LLVMLibCLibraryRules.cmake

foreach(dep IN LISTS all_deps)
     list(APPEND objects $<$<STREQUAL:$<TARGET_NAME_IF_EXISTS:${dep}>,${dep}>:$<TARGET_OBJECTS:${dep}>>)
   endforeach(dep)
 
   add_library(
     ${target_name}
     STATIC
     ${objects}
   )
-  set_target_properties(${target_name}  PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+  set_target_properties(${target_name} PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${LIBC_LIBRARY_DIR})
 endfunction(add_entrypoint_library)
 
 # Rule to build a shared library of redirector objects.
 function(add_redirector_library target_name)
   cmake_parse_arguments(
     "REDIRECTOR_LIBRARY"
     ""
     ""
function(add_redirector_library target_name)
   # TODO: Call the linker explicitly instead of calling the compiler driver to
   # prevent DT_NEEDED on C++ runtime.
   add_library(
     ${target_name}
     EXCLUDE_FROM_ALL
     SHARED
     ${obj_files}
   )
-  set_target_properties(${target_name}  PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+  set_target_properties(${target_name}  PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${LIBC_LIBRARY_DIR})
   target_link_libraries(${target_name}  -nostdlib -lc -lm)
   set_target_properties(${target_name}  PROPERTIES LINKER_LANGUAGE "C")
 endfunction(add_redirector_library)
 
 set(HDR_LIBRARY_TARGET_TYPE "HDR_LIBRARY")
 
 # Internal function, used by `add_header_library`.
 function(create_header_library fq_target_name)