add standard_temp_file

add standard_temp_file

This adds a new helper proc, standard_temp_file.  This proc takes a
file name and returns a possibly-qualified form.  This lets us make
parallel runs use a directory other than ".", which helps the inotify
mode.

This initial patch introduces the proc and changes a few spots to use
it.

	* lib/gdb.exp (standard_temp_file): New proc.
	(support_complex_tests, is_ilp32_target, is_lp64_target)
	(is_amd64_regs_target, skip_altivec_tests, skip_vsx_tests): Use
	standard_temp_file.