Give files from #line the characteristics of the current file

This allows #line directives to appear in system headers that have code
that clang would normally warn on. This is compatible with GCC, which is
easy to test by running `gcc -E`.

Fixes PR30752

llvm-svn: 303582
diff --git a/clang/lib/Lex/Pragma.cpp b/clang/lib/Lex/Pragma.cpp
index 99d5618..2d078a4 100644
--- a/clang/lib/Lex/Pragma.cpp
+++ b/clang/lib/Lex/Pragma.cpp
@@ -475,9 +475,9 @@
   // Emit a line marker.  This will change any source locations from this point
   // forward to realize they are in a system header.
   // Create a line note with this information.
-  SourceMgr.AddLineNote(SysHeaderTok.getLocation(), PLoc.getLine()+1,
+  SourceMgr.AddLineNote(SysHeaderTok.getLocation(), PLoc.getLine() + 1,
                         FilenameID, /*IsEntry=*/false, /*IsExit=*/false,
-                        /*IsSystem=*/true, /*IsExternC=*/false);
+                        SrcMgr::C_System);
 }
 
 /// HandlePragmaDependency - Handle \#pragma GCC dependency "foo" blah.