PR96493, powerpc local call linkage failure

PR96493, powerpc local call linkage failure

This corrects current_file_function_operand, an operand predicate used
to determine whether a symbol_ref is safe to use with the local_call
patterns.  Calls between pcrel and non-pcrel code need to go via
linker stubs.  In the case of non-pcrel code to pcrel the stub saves
r2 but there needs to be a nop after the branch for the r2 restore.
So the local_call patterns can't be used there.  For pcrel code to
non-pcrel the local_call patterns could still be used, but I thought
it better to not use them since the call isn't direct.  Code generated
by the corresponding call_nonlocal_aix for pcrel is identical anyway.

Incidentally, without the TREE_CODE () == FUNCTION_DECL test,
gcc.c-torture/compile/pr37433.c and pr37433-1.c ICE.  Also, if you
make the test more strict by disallowing an op without a
SYMBOL_REF_DECL then a bunch of go and split-stack tests fail.  That's
because a prologue call to __morestack can't have a following nop.
(__morestack calls its caller at a fixed offset from the __morestack
call!)

gcc/
	PR target/96493
	* config/rs6000/predicates.md (current_file_function_operand): Don't
	accept functions that differ in r2 usage.

gcc/testsuite/
	* gcc.target/powerpc/pr96493.c: New file.