gollvm: use the given triple string when it is specified

Not only the aliases, we should also use the given triple string
itself.

Change-Id: I8686a18eaa92b9fabdd73eed1676a6c3b3211623
Reviewed-on: https://go-review.googlesource.com/116220
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/driver/GccUtils.cpp b/driver/GccUtils.cpp
index 858731f..76b7171 100644
--- a/driver/GccUtils.cpp
+++ b/driver/GccUtils.cpp
@@ -162,6 +162,7 @@
     case llvm::Triple::x86:
     case llvm::Triple::x86_64:
       s.tripleAliases = {
+        triple_.str(),
         "x86_64-linux-gnu",       "x86_64-unknown-linux-gnu",
         "x86_64-pc-linux-gnu",    "x86_64-redhat-linux6E",
         "x86_64-redhat-linux",    "x86_64-suse-linux"