Teach the Linux toolchain about more modern Gentoo installations of GCC
which add another wrinkle to the installation of the libstdc++ headers.

Add at least some basic testing of the weirdnesses of Gentoo's layout.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189212 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ToolChains.h b/lib/Driver/ToolChains.h
index a37cf47..acfcfdf 100644
--- a/lib/Driver/ToolChains.h
+++ b/lib/Driver/ToolChains.h
@@ -50,6 +50,9 @@
     /// \brief The parsed major, minor, and patch numbers.
     int Major, Minor, Patch;
 
+    /// \brief The text of the parsed major, and major+minor versions.
+    std::string MajorStr, MinorStr;
+
     /// \brief Any textual suffix on the patch number.
     std::string PatchSuffix;