Compile texvccheck in testsuite

The MathInputCheckTexvcTest class expects texvccheck to be available
via $wgMathTexvcCheckExecutable.  It is not always set or the executable
might not have been compiled (for example on Wikimedia CI Jenkins).

This patch still attempt to use $wgMathTexvcCheckExecutable, if it is
not found it will attempt to compile it using the Makefile in the
texvccheck subfolder of the repository.  That should work whenever
someone has ocaml installed, the resulting binary is used to set
$wgMathTexvcCheckExecutable.

Bug: 61090
Change-Id: I9ea4b87de6e2827aad83961712f66ecbef2639de