[clang] [Driver] Teach Barmetal toolchain about GCC installation (PR #121829)

[Petr Hosek via cfe-commits]

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@@ -110,20 +110,81 @@ static std::string computeBaseSysRoot(const Driver &D, bool IncludeTriple) {
   return std::string(SysRootDir);
 }
 
+static bool hasGCCToolChainAlongSideClang(const Driver &D) {
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petrhosek wrote:

If understand correctly, this should cover the case when we're using newlib (and potentially libgcc and libstdc++) together with Clang (but not using `clang-runtimes`). @quic-garvgupt can you clarify this? If that's the case, then I think this function could use a better name. In either case, I agree with @smithp35 that this logic is fragile since `crt0.o` is commonly used by most C libraries.

https://github.com/llvm/llvm-project/pull/121829