Re: gdb: Improve formatting of 'show architecture' messages

Commit ccb9eba6 updated the testsuite for some targets without
running the testsuite on those targets.  This patch corrects the
update, in most cases just adding the expected full-stop.

On powerpc64le-linux, fixes these:
FAIL: gdb.arch/powerpc-d128-regs.exp: checking for PPC arch
FAIL: gdb.arch/powerpc-disassembler-options.exp: set architecture powerpc:common64
FAIL: gdb.arch/powerpc-disassembler-options.exp: set architecture rs6000:6000
FAIL: gdb.arch/ppc64-symtab-cordic.exp: show architecture

I also verified that arm-linuxeabi and s390x-linux cross-builds now
pass their disassembler-options.exp tests.

	* gdb.arch/arm-disassembler-options.exp: Adjust expected
	"target architecture" output.
	* gdb.arch/powerpc-d128-regs.exp: Likewise.
	* gdb.arch/powerpc-disassembler-options.exp: Likewise.
	* gdb.arch/ppc64-symtab-cordic.exp: Likewise.
	* gdb.arch/s390-disassembler-options.exp: Likewise.