Add a libLTO API to query a memory buffer and check if it contains ObjC categories

Add a libLTO API to query a memory buffer and check if it contains ObjC categories

The linker supports a feature to force load an object from a static
archive if it defines an Objective-C category.
This API supports this feature by looking at every section in the
module to find if a category is defined in the module.

llvm-svn: 275125