PR fortran/90903 [part2] - Add runtime checking for the MVBITS intrinsic

PR fortran/90903 [part2] - Add runtime checking for the MVBITS intrinsic

Implement inline expansion of the intrinsic elemental subroutine MVBITS
with optional runtime checks for valid argument range.

gcc/fortran/ChangeLog:

	* iresolve.c (gfc_resolve_mvbits): Remove unneeded conversion of
	FROMPOS, LEN and TOPOS arguments to fit a C int.
	* trans-intrinsic.c (gfc_conv_intrinsic_mvbits): Add inline
	expansion of MVBITS intrinsic elemental subroutine and add code
	for runtime argument checking.
	(gfc_conv_intrinsic_subroutine): Recognise MVBITS intrinsic, but
	defer handling to gfc_trans_call.
	* trans-stmt.c (replace_ss):
	(gfc_trans_call): Adjust to handle inline expansion, scalarization
	of intrinsic subroutine MVBITS in gfc_conv_intrinsic_mvbits.
	* trans.h (gfc_conv_intrinsic_mvbits): Add prototype for
	gfc_conv_intrinsic_mvbits.

gcc/testsuite/ChangeLog:

	* gfortran.dg/check_bits_2.f90: New test.

Co-authored-by: Paul Thomas  <pault@gcc.gnu.org>