add really really trivial #line support, where #line now makes every  location below it report as coming from the #line location.  For example, with:
add really really trivial #line support, where #line now makes every 
location below it report as coming from the #line location.  For example,
with:

#line 92 "foo.h"
#warning blarg!
#warning blarg!

we now emit:

foo.h:92:2: warning: #warning blarg!
#warning blarg!
 ^
foo.h:92:2: warning: #warning blarg!
#warning blarg!
 ^



git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@63709 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang