mail/cue: Fix compiler check via pkglint

AUTOFIX: hacks.mk:5: Replacing "${PKGSRC_COMPILER} == \"ido\"" with "${PKGSRC_COMPILER:Mido}".

The PKGSRC_COMPILER can be a list of chained compilers, e.g. "ccache
distcc clang". Therefore, comparing it using == or != leads to wrong
results in these cases.

(gdt)