Add limited build configuration support for testing against compiler submit versions. (rdar://problem/16337966)

This is meant to be utilized for a narrow set of scenarios specific to dogfooding our pre-1.0 compiler, so please do not take any dependencies on this.  In fact, I'll be removing this in the next milestone.  (See rdar://problem/16380797.)

Also included - improve error recovery when parsing broken build configuration clauses.

Swift SVN r15694

include/swift/Basic/Version.h

@@ -28,6 +28,8 @@ namespace version {
 /// includes the Swift version number, the repository version, and the vendor
 /// tag.
 std::string getSwiftFullVersion();
+  
+std::string getSwiftSubmitVersionQuad();
 
 } // end namespace version
 } // end namespace swift