Commits ecade1c, afbbc18, and a5a34d2 added compiler flags for
vmsplice, splice, and open_by_handle_at respectively on default
misc/Makefile. However such symbols are build only for Linux and
the rules should on linux Makefile only.
Checked on x86_64-linux-gnu.
* misc/Makefile (CFLAGS-vmsplice.c): Remove rule.
(CFLAGS-splice.c): Likewise.
(CFLAGS-open_by_handle_at.c): Likewise.
* sysdeps/unix/sysv/linux/Makefile (CFLAGS-vmsplice.c): New rule.
(CFLAGS-splice.c): Likewise.
(CFLAGS-open_by_handle_at.c): Likewise.