In generated Cminor functions, make sure local variables include

all x used as destination of a call [x = f(args)].  This wasn't true before
if x was a global C#minor variable.


git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1136 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e