m4macros: Use PKG_PROG_PKG_CONFIG

Signed-off-by: Simon McVittie <smcv@debian.org>
1 job for wip/smcv/ac-path-tool-2 in 30 minutes and 26 seconds (queued for 15 seconds)
Status Job ID Name Coverage
  Build
passed #18706
build

00:30:26