gollvm: use the same install dir handling for library search

CL 116655 makes it derive the install path from the executable
path, instead of hard-code it, and use it in package search.
Do the same for library search in linking.

Change-Id: Ia49ffd41fccdf26a025d9041358c72ba883068c6
Reviewed-on: https://go-review.googlesource.com/117256
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/driver/GnuTools.cpp b/driver/GnuTools.cpp
index 0525b52..ff33938 100644
--- a/driver/GnuTools.cpp
+++ b/driver/GnuTools.cpp
@@ -383,7 +383,7 @@
   // Pick up correct directory for Go libraries.
   std::string golib("-L");
+  golib += toolchain().driver().installedLibDir();
   if (useStdLib) {