Apply -fomit-frame-pointer only to .o/.os files

Since -fomit-frame-pointer is compatible with -pg, apply it only to
.o/.os files.

	* sysdeps/unix/sysv/linux/i386/Makefile (CFLAGS-epoll_pwait.c):
	Renamed to ...
	(CFLAGS-epoll_pwait.o): This.
	(CFLAGS-mmap.c): Renamed to ...
	(CFLAGS-mmap.o): This.
	(CFLAGS-mmap64.c): Renamed to ...
	(CFLAGS-mmap64.o): This.
	(CFLAGS-epoll_pwait.os): New.
	(CFLAGS-mmap.os): Likewise.
	(CFLAGS-mmap64.os): Likewise.
	(CFLAGS-semtimedop.os): Likewise.
	(CFLAGS-semtimedop.c): Renamed to ...
	(CFLAGS-semtimedop.o): This.