Makefile: fixup linker flags usage
Makefile: fixup linker flags usage

These are linker commands, not compiler (even though we use CC as LD).
Use LDLIBS consistently, and don't provide CFLAGS.

This improves clarity and consistency, even if it still doesn't truly
separate CC and LD.

BUG=none
TEST=build

Cq-Depend: chromium:2285152
Signed-off-by: Brian Norris <67059238af8e1945c40edb274ce1d51ba595dbf3@chromium.org>
Change-Id: Ie54fafdccab5b9c942fc2cc38009c75f3d46a5e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2281964
Reviewed-by: Joel Kitching <c2feea8c1334a0d339e816ae4c7c9ecfa9b30a91@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot