PR modula2/115276 bugfix libgm2 wraptime.InitTM returns NIL

PR modula2/115276 bugfix libgm2 wraptime.InitTM returns NIL

This patch fixes libgm2/libm2iso/wraptime.cc:InitTM so that
it does not always return NULL.  The incorrect autoconf macro
was used (inside InitTM) and the function short circuited
to return NULL.  The fix is to use HAVE_SYS_TIME_H and use
AC_HEADER_TIME in libgm2/configure.ac.

libgm2/ChangeLog:

	PR modula2/115276
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Use AC_HEADER_TIME.
	* libm2iso/wraptime.cc (InitTM): Check HAVE_SYS_TIME_H
	before using struct tm to obtain the size.

gcc/testsuite/ChangeLog:

	PR modula2/115276
	* gm2/isolib/run/pass/testinittm.mod: New test.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>