Subject:  Fix missing stddef.h
Patch author:  Orson Teodoro <orsonteodoro@hotmail.com>
Date: Sat Mar 12 04:48:36 PM PST 2022 (Unix time: 1647132516)
--- a/lib/Driver/ToolChains/Gnu.cpp.orig	2022-10-01 01:20:16.935752721 -0700
+++ b/lib/Driver/ToolChains/Gnu.cpp	2022-10-01 01:24:04.025567570 -0700
@@ -3031,6 +3031,11 @@ void Generic_GCC::AddMultilibIncludeArgs
   addSystemInclude(DriverArgs, CC1Args,
                    Twine(LibPath) + "/../" + GCCTriple.str() + "/include");
 
+  // For stddef.h on Gentoo
+  StringRef InstallDir = GCCInstallation.getInstallPath();
+  addSystemInclude(DriverArgs, CC1Args,
+                   InstallDir.str() + "/include");
+
   const auto &Callback = Multilibs.includeDirsCallback();
   if (Callback) {
     for (const auto &Path : Callback(GCCInstallation.getMultilib()))
