improve the 'conflicting types' diagnostics to include correct location info, now

that it is plumbed through Sema.  On a file from growl, we used to emit:

t.mi:107059:1: warning: conflicting types for 'removePluginHandler:forPluginTypes:'
- (void) removePluginHandler:(id <GrowlPluginHandler>)handler forPluginTypes:(NSSet *)extensions {
^
t.mi:105280:1: note: previous definition is here
- (void) removePluginHandler:(id <NSObject>)handler forPluginTypes:(NSSet *)types;
^

now we produce:

t.mi:107059:55: warning: conflicting parameter types in implementation of 'removePluginHandler:forPluginTypes:': 'id<NSObject>' vs 'id<GrowlPluginHandler>'
- (void) removePluginHandler:(id <GrowlPluginHandler>)handler forPluginTypes:(NSSet *)extensions {
                                                      ^
t.mi:105280:45: note: previous definition is here
- (void) removePluginHandler:(id <NSObject>)handler forPluginTypes:(NSSet *)types;
                                            ^

We still don't have proper loc info for properties, hence the FIXME.

rdar://6782494

llvm-svn: 68879