devel/tex-web2c may have a build race associated with mplib.h for libmplibbackends_a-pngout.o and libmplibbackends_a-svgout.o

From: Mark Millard <marklmi_at_yahoo.com>
Date: Tue, 19 Sep 2023 15:28:32 UTC
I got the following while poudriere-devel was doing a build:

--- libmplibbackends_a-pngout.o ---
mplibdir/pngout.w:63:10: fatal error: 'mplib.h' file not found
#include "mplib.h"
         ^~~~~~~~~
--- libmplibbackends_a-svgout.o ---
mplibdir/svgout.w:63:10: fatal error: 'mplib.h' file not found
#include "mplib.h"
         ^~~~~~~~~

A simple re-run of the build did not get any errors.

===
Mark Millard
marklmi at yahoo.com