A user may configure `LDFLAGS` but not `LD`. When choosing a linker, we
will prefer `ldd`, then `ld.gold`, then `ld.bfd` -- however, we have to
check for a working linker. If either of these fail, we try the next in
line.

However, we were not considering the `$LDFLAGS` when checking if these
linkers worked. So we would pick a linker that does not support the
current $LDFLAGS and fail further down the line when we used that linker
with those flags.

Fixes #24565, where `LDFLAGS=-Wl,-z,pack-relative-relocs` is not
supported by `ld.gold` but that was being picked still.