[libc] Only enable LLVM_FULL_BUILD_MODE by default for GPU targets (#84664)

Summary:
Currently we have a conditional that turns the full build on by default
if it is a default target. This used to work fine when the GPU was the
only target that was ever present. However, we've recently changed to
allow building multiple of these at the same time. That means we should
have the ability to build overlay mode in the CPU mode and full build in
the GPU mode. This patch makes some simple adjustments to pass the
arguments per-triple. This slightly extends the existing `-DRUNTIMES_`
argument support to also transform any extra CMake inputs rather than
just the passed CMake variables.

Author: jhuber6

llvm/CMakeLists.txt

@@ -173,16 +173,15 @@ endforeach()
 set(NEED_LIBC_HDRGEN FALSE)
 if("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
   set(NEED_LIBC_HDRGEN TRUE)
-else()
-  foreach(_name ${LLVM_RUNTIME_TARGETS})
-    if("libc" IN_LIST RUNTIMES_${_name}_LLVM_ENABLE_RUNTIMES)
-      set(NEED_LIBC_HDRGEN TRUE)
-      if("${_name}" STREQUAL "amdgcn-amd-amdhsa" OR "${_name}" STREQUAL "nvptx64-nvidia-cuda")
-        set(LLVM_LIBC_GPU_BUILD ON)
-      endif()
-    endif()
-  endforeach()
 endif()
+foreach(_name ${LLVM_RUNTIME_TARGETS})
+  if("libc" IN_LIST RUNTIMES_${_name}_LLVM_ENABLE_RUNTIMES)
+    set(NEED_LIBC_HDRGEN TRUE)
+    if("${_name}" STREQUAL "amdgcn-amd-amdhsa" OR "${_name}" STREQUAL "nvptx64-nvidia-cuda")
+      set(LLVM_LIBC_GPU_BUILD ON)
+    endif()
+  endif()
+endforeach()
 if(NEED_LIBC_HDRGEN)
   # To build the libc runtime, we need to be able to build few libc build
   # tools from the "libc" project. So, we add it to the list of enabled

llvm/runtimes/CMakeLists.txt

@@ -358,6 +358,14 @@ function(runtime_register_target name)
         endif()
       endif()
     endforeach()
+    foreach(variable_name ${${name}_extra_args})
+      string(FIND "${variable_name}" "-DRUNTIMES_${extra_name}_" out)
+      if("${out}" EQUAL 0)
+        string(REPLACE "-DRUNTIMES_${extra_name}_" "" new_name ${variable_name})
+        string(REPLACE ";" "|" new_value "${new_name}")
+        list(APPEND ${name}_extra_args "-D${new_value}")
+      endif()
+    endforeach()
   endforeach()
 
   set_enable_per_target_runtime_dir()
@@ -438,21 +446,29 @@ if(runtimes)
     if(NOT hdrgen_exe)
       message(FATAL_ERROR "libc-hdrgen executable missing")
     endif()
-    set(libc_cmake_args "-DLIBC_HDRGEN_EXE=${hdrgen_exe}"
-                        "-DLLVM_LIBC_FULL_BUILD=ON")
+    list(APPEND libc_cmake_args "-DLIBC_HDRGEN_EXE=${hdrgen_exe}")
     list(APPEND extra_deps ${hdrgen_deps})
-    if(LLVM_LIBC_GPU_BUILD)
-      list(APPEND libc_cmake_args "-DLLVM_LIBC_GPU_BUILD=ON")
-      # The `libc` project may require '-DCUDAToolkit_ROOT' in GPU mode.
-      if(CUDAToolkit_ROOT)
-        list(APPEND libc_cmake_args "-DCUDAToolkit_ROOT=${CUDAToolkit_ROOT}")
-      endif()
-      foreach(dep clang-offload-packager nvptx-arch amdgpu-arch)
-        if(TARGET ${dep})
-          list(APPEND extra_deps ${dep})
-        endif()
-      endforeach()
+  endif()
+  if(LLVM_LIBC_GPU_BUILD)
+    list(APPEND libc_cmake_args "-DLLVM_LIBC_GPU_BUILD=ON")
+    if("libc" IN_LIST RUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES)
+      list(APPEND libc_cmake_args "-DRUNTIMES_amdgcn-amd-amdhsa_LLVM_LIBC_FULL_BUILD=ON")
     endif()
+    if("libc" IN_LIST RUNTIMES_nvptx64-nvidia-cuda_LLVM_ENABLE_RUNTIMES)
+      list(APPEND libc_cmake_args "-DRUNTIMES_nvptx64-nvidia-cuda_LLVM_LIBC_FULL_BUILD=ON")
+    endif()
+    # The `libc` project may require '-DCUDAToolkit_ROOT' in GPU mode.
+    if(CUDAToolkit_ROOT)
+      list(APPEND libc_cmake_args "-DCUDAToolkit_ROOT=${CUDAToolkit_ROOT}")
+    endif()
+    foreach(dep clang-offload-packager nvptx-arch amdgpu-arch)
+      if(TARGET ${dep})
+        list(APPEND extra_deps ${dep})
+      endif()
+    endforeach()
+  endif()
+  if(LLVM_LIBC_FULL_BUILD)
+    list(APPEND libc_cmake_args "-DLLVM_LIBC_FULL_BUILD=ON")
   endif()
   if(NOT LLVM_RUNTIME_TARGETS)
     runtime_default_target(