MFH: r525281

glib20: revert SSP_CFLAGS workaround (ports r500819)

This was later diagnosed to be a bug in libc, which has since been addressed
in all supported releases and branches. PORTREVISION is bumped as SSP_CFLAGS
will change the output.

The bug was fixed in the following patch levels (FreeBSD-EN-20:01.ssp):

• 12.1-p2
• 12.0-p13
• 11.3-p6

PR: 243735
Approved by: kwm (gnome, maintainer via IRC)

Approved by: ports-secteam (miwi)