bsd.sites.mk: Update all ports using USE_GITLAB

Replace GL_COMMIT by GL_TAGNAME in all ports. The new GL_TAGNAME is
backwards-compatible (accepting any commit hash as before), but also
understands an actual tag name. Moving to tag names where appropriate is
left to individual ports' maintainers.

Approved by:		portmgr (tcberner, mentor)
Differential Revision:	https://reviews.freebsd.org/D37077