Teach header search about GCC 4.9 header search paths in Gentoo, they
now use the full GCC version in their weird suffix.

llvm-svn: 268874
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index f905b5d..1bf17e4 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -4134,6 +4134,7 @@
   const std::string LibStdCXXIncludePathCandidates[] = {
       // Gentoo is weird and places its headers inside the GCC install,
       // so if the first attempt to find the headers fails, try these patterns.
+      InstallDir.str() + "/include/g++-v" + Version.Text,
       InstallDir.str() + "/include/g++-v" + Version.MajorStr + "." +
           Version.MinorStr,
       InstallDir.str() + "/include/g++-v" + Version.MajorStr,