diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -515,6 +515,10 @@
 
 Specify comma-separated list of offloading target triples (CUDA and HIP only)
 
+.. option:: --overlay-platform-toolchain=<arg>
+
+Specify a toolchain with higher priority than sysroot in search paths.
+
 .. option:: -p, --profile
 
 .. option:: -pagezero\_size<arg>
diff --git a/clang/include/clang/Driver/Driver.h b/clang/include/clang/Driver/Driver.h
--- a/clang/include/clang/Driver/Driver.h
+++ b/clang/include/clang/Driver/Driver.h
@@ -149,6 +149,9 @@
   typedef SmallVector<std::string, 4> prefix_list;
   prefix_list PrefixDirs;
 
+  /// Alternative toolchain path used prior to sysroot.
+  std::string OverlayToolChainPath;
+
   /// sysroot, if present
   std::string SysRoot;
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4180,6 +4180,8 @@
 def _output_class_directory : Separate<["--"], "output-class-directory">, Alias<foutput_class_dir_EQ>;
 def _output_EQ : Joined<["--"], "output=">, Alias<o>;
 def _output : Separate<["--"], "output">, Alias<o>;
+def _overlay_platform_toolchain_EQ : Joined<["--"], "overlay-platform-toolchain=">;
+def _overlay_platform_toolchain : Separate<["--"], "overlay-platform-toolchain">, Alias<_overlay_platform_toolchain_EQ>;
 def _param : Separate<["--"], "param">, Group<CompileOnly_Group>;
 def _param_EQ : Joined<["--"], "param=">, Alias<_param>;
 def _precompile : Flag<["--"], "precompile">, Flags<[NoXarchOption]>,
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1208,6 +1208,11 @@
       CompilerPath = Split.second;
     }
   }
+  if (const Arg *A =
+          Args.getLastArg(options::OPT__overlay_platform_toolchain_EQ)) {
+    OverlayToolChainPath = A->getValue();
+    DyldPrefix = A->getValue();
+  }
   if (const Arg *A = Args.getLastArg(options::OPT__sysroot_EQ))
     SysRoot = A->getValue();
   if (const Arg *A = Args.getLastArg(options::OPT__dyld_prefix_EQ))
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1867,6 +1867,10 @@
   if (A)
     return A->getValue();
 
+  if (const Arg *X = Args.getLastArg(
+          clang::driver::options::OPT__overlay_platform_toolchain_EQ))
+    return X->getValue();
+
   // If we have a SysRoot, ignore GCC_INSTALL_PREFIX.
   // GCC_INSTALL_PREFIX specifies the gcc installation for the default
   // sysroot and is likely not valid with a different sysroot.
diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -260,6 +260,14 @@
 
   const std::string OSLibDir = std::string(getOSLibDir(Triple, Args));
   const std::string MultiarchTriple = getMultiarchTriple(D, Triple, SysRoot);
+  const std::string &ExtraPath = D.OverlayToolChainPath;
+
+  if (!D.OverlayToolChainPath.empty()) {
+    addPathIfExists(D, ExtraPath + "/lib/" + MultiarchTriple, Paths);
+    addPathIfExists(D, ExtraPath + "/lib/../" + OSLibDir, Paths);
+    addPathIfExists(D, ExtraPath + "/usr/lib/" + MultiarchTriple, Paths);
+    addPathIfExists(D, ExtraPath + "/usr/lib/../" + OSLibDir, Paths);
+  }
 
   // mips32: Debian multilib, we use /libo32, while in other case, /lib is
   // used. We need add both libo32 and /lib.
@@ -314,6 +322,11 @@
       addPathIfExists(D, D.Dir + "/../" + OSLibDir, Paths);
   }
 
+  if (!D.OverlayToolChainPath.empty()) {
+    addPathIfExists(D, ExtraPath + "/lib", Paths);
+    addPathIfExists(D, ExtraPath + "/usr/lib", Paths);
+  }
+
   addPathIfExists(D, SysRoot + "/lib", Paths);
   addPathIfExists(D, SysRoot + "/usr/lib", Paths);
 }
@@ -567,6 +580,10 @@
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
+  if (!D.OverlayToolChainPath.empty())
+    addExternCSystemInclude(DriverArgs, CC1Args,
+                            D.OverlayToolChainPath + "/include");
+
   // LOCAL_INCLUDE_DIR
   addSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/local/include");
   // TOOL_INCLUDE_DIR
diff --git a/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0/include/.keep b/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0/include/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib64/.keep b/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib64/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0/include/.keep b/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0/include/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0/lib/gcc/powerpc64le-linux-gnu/8.3.0/.keep b/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0/lib/gcc/powerpc64le-linux-gnu/8.3.0/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0/lib64/.keep b/clang/test/Driver/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0/lib64/.keep
new file mode 100644
diff --git a/clang/test/Driver/overlay-toolchain.cpp b/clang/test/Driver/overlay-toolchain.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/overlay-toolchain.cpp
@@ -0,0 +1,18 @@
+// RUN: %clangxx %s -### --target=powerpc64le-linux-gnu \
+// RUN:   --overlay-platform-toolchain=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0 \
+// RUN:   2>&1 | FileCheck %s --check-prefix=OVERLAY
+// RUN: %clangxx %s -### --target=powerpc64le-linux-gnu \
+// RUN:   --sysroot=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-8.3.0 \
+// RUN:   --overlay-platform-toolchain=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0 \
+// RUN:   2>&1 | FileCheck %s --check-prefixes=OVERLAY,ROOT
+
+// OVERLAY: "-internal-externc-isystem"
+// OVERLAY: "[[TOOLCHAIN:[^"]+]]/powerpc64le-linux-gnu-tree/gcc-11.2.0/include"
+// ROOT: "-internal-externc-isystem"
+// ROOT: "[[TOOLCHAIN]]/powerpc64le-linux-gnu-tree/gcc-8.3.0/include"
+// OVERLAY: "-dynamic-linker"
+// OVERLAY: "[[TOOLCHAIN]]/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib64/ld64.so.2"
+// OVERLAY: "-L[[TOOLCHAIN]]/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib/../lib64"
+// ROOT: "-L[[TOOLCHAIN]]/powerpc64le-linux-gnu-tree/gcc-8.3.0/lib/../lib64"
+// OVERLAY: "-L[[TOOLCHAIN]]/powerpc64le-linux-gnu-tree/gcc-11.2.0/lib"
+// ROOT: "-L[[TOOLCHAIN]]/powerpc64le-linux-gnu-tree/gcc-8.3.0/lib"