When adding a dSYM to an existing ObjectFile, we can have a situation
with binaries in the dyld shared cache (esp on iOS) where the file
address for the executable binary (maybe from memory, maybe from
an expanded copy of the dyld shared cache) is different from the
file address in the dSYM.  In that case, ObjectFileMachO replaces
the file addresses from the original binary with the dSYM file
addresses (usually 0-based) -- lldb doesn't have a notion of two
file addresses for a given module so they need to agree.

There was a cache of file addresses over in the Symtab so I added
a method to the Module and the objects within to clear any file address
caches if they exist, and added an implementation in the Symtab
module to do that.
<rdar://problem/16929569>