sysutils/mcelog: Fix DF build by respecting CFLAGS and USE+=alias

PR:		194825
Submitted by:	ftigeot
Approved by:	maintainer (Jeremy Chadwick)


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@372212 35697150-7ecd-e111-bb59-0022644237b5