S390: Fix compiler invocation with "compile" command

S390: Fix compiler invocation with "compile" command

On 64-bit S390 platforms the "compile" command always failed because
gcc was not invoked correctly.  This patch fixes the compiler
invocation.

gdb/ChangeLog:

	* s390-linux-tdep.c (s390_gcc_target_options): Not just handle
	31-bit targets, but 64-bit targets as well.
	(s390_gnu_triplet_regexp): New function.
	(s390_gdbarch_init): Set the gcc_target_options gdbarch method for
	64-bit targets as well.  Set the gnu_triplet_regexp gdbarch
	method.