Fixed the MCJIT so that it can emit not only instance

methods but also class methods for Objective-C.

Clang emits Objective-C method names with '\1' at the
beginning, and the JIT has pre-existing logic to try
prepending a '\1' when searching a module for an
instance method (that is, a method whose name begins
with '-').  I simply extended it to do the same thing
when it encountered a class method (a method whose
name begins with '+').

llvm-svn: 144451