[CMake][Fuchsia] Enable libc++ in the baremetal build (#95017)

For now, we include headers and don't use libc++abi.

Author: petrhosek

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -328,9 +328,24 @@ foreach(target armv6m-unknown-eabi)
   endforeach()
   set(RUNTIMES_${target}_LLVM_LIBC_FULL_BUILD ON CACHE BOOL "")
   set(RUNTIMES_${target}_LIBC_ENABLE_USE_BY_CLANG ON CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_CXX_ABI none CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_LOCALIZATION OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_UNICODE OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_WIDE_CHARACTERS OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_THREADS OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_INSTALL_LIBRARY OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
   set(RUNTIMES_${target}_LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
-  set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "libc" CACHE STRING "")
+  set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "libc;libcxx" CACHE STRING "")
 endforeach()
 
 foreach(target riscv32-unknown-elf)
@@ -361,9 +376,24 @@ foreach(target riscv32-unknown-elf)
   endforeach()
   set(RUNTIMES_${target}_LLVM_LIBC_FULL_BUILD ON CACHE BOOL "")
   set(RUNTIMES_${target}_LIBC_ENABLE_USE_BY_CLANG ON CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_CXX_ABI none CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_LOCALIZATION OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_UNICODE OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_WIDE_CHARACTERS OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_THREADS OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_INSTALL_LIBRARY OFF CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
   set(RUNTIMES_${target}_LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
-  set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "libc" CACHE STRING "")
+  set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "libc;libcxx" CACHE STRING "")
 endforeach()
 
 set(LLVM_BUILTIN_TARGETS "${BUILTIN_TARGETS}" CACHE STRING "")