[Basic] Use start loc for original source range in isBeforeInSource

Given we're working with CharSourceRanges, the end location is past
the end of the actual range, so when checking if e.g a function body
macro is contained within the function decl, we fail since the end
location is past the closing `}`. Check the start location instead,
which is part of the range.

Author: hamishknight

lib/Basic/SourceLoc.cpp

@@ -836,11 +836,11 @@ static bool isBeforeInSource(
   SourceLoc firstLocInLCA = firstMismatch == firstAncestors.end()
       ? firstLoc
       : sourceMgr.getGeneratedSourceInfo(*firstMismatch)
-          ->originalSourceRange.getEnd();
+          ->originalSourceRange.getStart();
   SourceLoc secondLocInLCA = secondMismatch == secondAncestors.end()
       ? secondLoc
       : sourceMgr.getGeneratedSourceInfo(*secondMismatch)
-          ->originalSourceRange.getEnd();
+          ->originalSourceRange.getStart();
   return sourceMgr.isBeforeInBuffer(firstLocInLCA, secondLocInLCA) ||
     (allowEqual && firstLocInLCA == secondLocInLCA);
 }