[Clang][Driver] Fix the missing Target-Triple-Level include path resolution in Baremetal Driver

The current baremetal driver implementation does not have a way to
derive the target-triple-level include path within the sysroot.

This feature is especially useful in setups where header paths
deviate from the default bare-metal assumptions. For example,
when headers are shared across target triples, it becomes necessary
to organize them under target-triple-specific directories to ensure
correct resolution..

Author: simpal01

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -408,6 +408,8 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
+  const Driver &D = getDriver();
+
   if (std::optional<std::string> Path = getStdlibIncludePath())
     addSystemInclude(DriverArgs, CC1Args, *Path);
 
@@ -418,6 +420,13 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
       llvm::sys::path::append(Dir, M.includeSuffix());
       llvm::sys::path::append(Dir, "include");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
+
+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, getTripleString());
+      if (D.getVFS().exists(Dir)) {
+        llvm::sys::path::append(Dir, "include");
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      }
     }
   }
 }
@@ -498,9 +507,13 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
         addSystemInclude(DriverArgs, CC1Args, TargetDir.str());
         break;
       }
-      // Add generic path if nothing else succeeded so far.
+      // Add generic paths if nothing else succeeded so far.
       llvm::sys::path::append(Dir, "include", "c++", "v1");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, Target, "include", "c++", "v1");
+      if (D.getVFS().exists(Dir))
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
       break;
     }
     case ToolChain::CST_Libstdcxx: {