[PATCH] [Driver] Support -muclibc / -mglibc command line options

[Rafael Ávila de Espíndola]

LGTM with a nit.

================
Comment at: lib/Driver/ToolChains.cpp:1739
@@ +1738,3 @@
+        if (StringRef(M.includeSuffix()).startswith("/uclibc"))
+          Dirs.push_back(
+              (InstallDir + "/../../../../sysroot/uclibc/usr/include").str());
----------------
Since you are calling str() anyway, it might be cleaner to construct it with

  String S = InstallDir + "/../../../../sysroot/";
  if (...)
    S +=
   else
     S +=

http://reviews.llvm.org/D4790