Add support for distros that like x86_64-unknown-linux-gnu.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@119425 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index 10a5597..d05b9e4 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -1329,6 +1329,8 @@
   } else if (Arch == llvm::Triple::x86_64) {
     if (llvm::sys::Path("/usr/lib/gcc/x86_64-linux-gnu").exists())
       GccTriple = "x86_64-linux-gnu";
+    else if (llvm::sys::Path("/usr/lib/gcc/x86_64-unknown-linux-gnu").exists())
+      GccTriple = "x86_64-unknown-linux-gnu";
     else if (llvm::sys::Path("/usr/lib/gcc/x86_64-pc-linux-gnu").exists())
       GccTriple = "x86_64-pc-linux-gnu";
     else if (llvm::sys::Path("/usr/lib/gcc/x86_64-redhat-linux").exists())