Make Gentoo GNU GCC Config override whitespace tolerant

The config-*triple* file handling isn't tolerant of 
leading/trailing whitespace, making it not terribly 
obvious when a single extraneous tab/space/etc will 
cause the override to be ignored. This patch simply 
trims the lines to ensure that it is tolerant of 
whitespace.

llvm-svn: 300328

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -2173,6 +2173,7 @@ bool Generic_GCC::GCCInstallationDetector::ScanGentooGccConfig(
     SmallVector<StringRef, 2> Lines;
     File.get()->getBuffer().split(Lines, "\n");
     for (StringRef Line : Lines) {
+      Line = Line.trim();
       // CURRENT=triple-version
       if (Line.consume_front("CURRENT=")) {
         const std::pair<StringRef, StringRef> ActiveVersion =