[clang] [Driver] Teach Barmetal toolchain about GCC installation(1/3) (PR #121829)

[Garvit Gupta via cfe-commits]

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@@ -110,20 +111,93 @@ static std::string computeBaseSysRoot(const Driver &D, bool IncludeTriple) {
   return std::string(SysRootDir);
 }
 
+// GCC sysroot here means form sysroot from either --gcc-install-dir, or from
+// --gcc-toolchain or if the toolchain is installed alongside clang in
+// bin/../<TargetTriple> directory if it is not explicitly specified on the
+// command line through `--sysroot` option. libc here will be newlib.
+std::string BareMetal::computeGCCSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  SmallString<128> SysRootDir;
+  if (GCCInstallation.isValid()) {
+    StringRef LibDir = GCCInstallation.getParentLibPath();
+    StringRef TripleStr = GCCInstallation.getTriple().str();
+    llvm::sys::path::append(SysRootDir, LibDir, "..", TripleStr);
+  } else {
+    // Use the triple as provided to the driver. Unlike the parsed triple
+    // this has not been normalized to always contain every field.
+    llvm::sys::path::append(SysRootDir, getDriver().Dir, "..",
+                            getDriver().getTargetTriple());
+  }
+
+  if (!llvm::sys::fs::exists(SysRootDir))
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quic-garvgupt wrote:

 I understand that. However, to preserve the behavior of both the BareMetal and RISCVToolchain objects, I need to maintain this condition. If this returns empty, only then does the control transfer to compute the sysroot, as it was done previously in the BareMetal toolchain. (See line 152 under `BareMetal::computeSysRoot()` function)

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