Split isFromMainFile into two functions.

Basically, isInMainFile considers line markers, and isWrittenInMainFile
doesn't.  Distinguishing between the two is useful when dealing with
files which are preprocessed files or rewritten with -frewrite-includes
(so we don't, for example, print useless warnings).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188968 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Rewrite/Frontend/RewriteMacros.cpp b/lib/Rewrite/Frontend/RewriteMacros.cpp
index 3c1d2e1..4f6a93f 100644
--- a/lib/Rewrite/Frontend/RewriteMacros.cpp
+++ b/lib/Rewrite/Frontend/RewriteMacros.cpp
@@ -115,7 +115,7 @@
     SourceLocation PPLoc = SM.getExpansionLoc(PPTok.getLocation());
 
     // If PPTok is from a different source file, ignore it.
-    if (!SM.isFromMainFile(PPLoc)) {
+    if (!SM.isWrittenInMainFile(PPLoc)) {
       PP.Lex(PPTok);
       continue;
     }