[clang] [Clang] Add clang flag --cstdlib (PR #183254)

[Volodymyr Turanskyy via cfe-commits]

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@@ -194,6 +194,7 @@ class ToolChain {
   mutable std::optional<CXXStdlibType> cxxStdlibType;
   mutable std::optional<RuntimeLibType> runtimeLibType;
   mutable std::optional<UnwindLibType> unwindLibType;
+  mutable std::optional<std::string> cstdlibType;
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voltur01 wrote:

Hi, the trade-off was discussed in the Embedded Working Group last week https://discourse.llvm.org/t/llvm-embedded-toolchains-working-group-sync-up/63270/90 - there was no clear conclusion though.

>From Arm Toolchain point of view a string would be simpler, however we only use the three libraries (LLVM libc, picolibc and newlib) that are already supported by LLVM, e.g. in libc++, so hopefully will be included into the enum from the beginning.

https://github.com/llvm/llvm-project/pull/183254