[libclang] Introduce clang_Cursor_getObjCSelectorIndex() function.

After getting a cursor with clang_getCursor for a particular source location,
allows querying the cursor in order to find out if the location points to a
selector identifier in an objc method or message expression, and which selector index it is.

rdar://11158946

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153781 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index c63a969..1896132 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -4425,6 +4425,10 @@
   
   return C;
 }
+
+int clang_Cursor_getObjCSelectorIndex(CXCursor cursor) {
+  return cxcursor::getSelectorIdentifierIndexAndLoc(cursor).first;
+}
   
 unsigned clang_getNumOverloadedDecls(CXCursor C) {
   if (C.kind != CXCursor_OverloadedDeclRef)