ObjC kindof: order the methods in global pool relative to availability.

ObjC kindof: order the methods in global pool relative to availability.

r265877 tries to put methods that are deprecated or unavailable to the
front of the global pool to emit diagnostics, but it breaks some of
our existing codes that depend on choosing a certain method for id
lookup.

This commit orders the methods with the same declaration with respect
to the availability, but do not order methods with different declaration.

rdar://25707511

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@266264 91177308-0d34-0410-b5e6-96231b3b80d8