[llvm] [flang-rt] Add support for using LLVM in-tree libc/libc++ (PR #131695)

[Michael Kruse via llvm-commits]

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@@ -244,6 +255,18 @@ check_cxx_compiler_flag("-UTESTFLAG" FLANG_RT_SUPPORTS_UNDEFINE_FLAG)
 # Check whether -fno-lto is supported.
 check_cxx_compiler_flag(-fno-lto FLANG_RT_HAS_FNO_LTO_FLAG)
 
+# Check whether -nostdlibinc is supported.
+check_cxx_compiler_flag(-nostdlibinc FLANG_RT_HAS_NOSTDLIBINC_FLAG)
+
+# Check whether -nostdlib is supported.
+check_cxx_compiler_flag(-nostdlib FLANG_RT_HAS_NOSTDLIB_FLAG)
+
+# Check whether -nostdinc++ is supported.
+check_cxx_compiler_flag(-nostdinc++ FLANG_RT_HAS_NOSTDINCXX_FLAG)
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Meinersbur wrote:

`-nostdinc++` aleady tested here: https://github.com/llvm/llvm-project/blob/main/runtimes/CMakeLists.txt#L156-L162

https://github.com/llvm/llvm-project/pull/131695