configure: Remove dead code

configure: Remove dead code

It appears as though the intent of this code is to define abort() and main()
symbols for some configure tests. However, it never gets used because the if
is only entered when not building for *-emu, but the next if block only runs
when building for *-emu. And the if block after that unconditionally resets
CFLAGS. So this code can have no effect.

Additionally, s/aclocal.m4/acinclude.m4/ and move grub_ASM_USCORE to put
with other marcos defined in acinclude.m4.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>