Move compile object files to compile subdirectory

Move compile object files to compile subdirectory

Move the object files corresponding to compile/*.c to the compile
subdirectory in the build tree.

ChangeLog
2017-11-27  Tom Tromey  <tom@tromey.com>

	* Makefile.in (SUBDIR_GCC_COMPILE_OBS): Redefine.
	(%.o): Remove compile rule.
	(CONFIG_SRC_SUBDIR): Add compile.