[committed] Fix compilation of testglue wrapper after c23 changes

testglue.c (which is used for exit/abort wrappers in the testsuite) isn't c23
compatible.   The testing harness tries to build testglue.c and use it, but
doesn't report a failure if the build fails, instead it's just not used.  As a
result we get all kinds of failures on targets which depend on testglue to
report back simulator status -- like tens of thousands of execution failures.

This patch just adds -std=gnu17 to the command line to build testglue.c.

There's other fallout from the c23 change..  My tester is chewing through
things right now...

Installing on the trunk.

testsuite
	* lib/wrapper.exp (${tool}_maybe_build_wrapper): Pass -std=gnu17 flag
	to build testglue wrapper.