Add missing stdlib.h includes to sim

This updates the various "mloop.in" files to emit an include of
stdlib.h, to avoid warnings about 'abort' being undeclared.

One such warning now remains, in mn10300.igen.  I don't know offhand
the best way to fix this one.

2021-05-04  Tom Tromey  <tromey@adacore.com>

	* mloop.in: Include <stdlib.h>.

sim/iq2000/ChangeLog
2021-05-04  Tom Tromey  <tromey@adacore.com>

	* mloop.in: Include <stdlib.h>.

sim/lm32/ChangeLog
2021-05-04  Tom Tromey  <tromey@adacore.com>

	* mloop.in: Include <stdlib.h>.

sim/m32r/ChangeLog
2021-05-04  Tom Tromey  <tromey@adacore.com>

	* mloop.in: Include <stdlib.h>.

sim/or1k/ChangeLog
2021-05-04  Tom Tromey  <tromey@adacore.com>

	* mloop.in: Include <stdlib.h>.