chore, rename PKG_CHECK_VAR -> PKG_CHECK_VAR_MSG (to avoid naming conflict)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>

Conflicts:
	configure.ac
minor, extend PKG_CHECK_VAR_MSG functionality to match pkg-config's PKG_CHECK_VAR

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, kick mxml check from c.ac

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'bld/dist' into next

* bld/dist:
  chore, kick mxml check from c.ac
  minor, extend PKG_CHECK_VAR_MSG functionality to match pkg-config's PKG_CHECK_VAR
  chore, rename PKG_CHECK_VAR -> PKG_CHECK_VAR_MSG (to avoid naming conflict)