A recent change broke bootstrap on ia32 because code intended to strip 
non-type-identity attributes from template arguments was also stripping 
type-identity attributes such as the ia32 calling convention attributes. 
   When I fixed that it reminded me of this bug: we weren't mangling the 
function pointer type differently based on the calling convention.  This 
patch fixes that.

Tested x86_64-pc-linux-gnu, applying to trunk.