Fortran: check POS and LEN arguments simplifying bit intrinsics [PR105986]

Fortran: check POS and LEN arguments simplifying bit intrinsics [PR105986]

gcc/fortran/ChangeLog:

	PR fortran/105986
	* simplify.cc (gfc_simplify_btest): Add check for POS argument.
	(gfc_simplify_ibclr): Add check for POS argument.
	(gfc_simplify_ibits): Add check for POS and LEN arguments.
	(gfc_simplify_ibset): Add check for POS argument.

gcc/testsuite/ChangeLog:

	PR fortran/105986
	* gfortran.dg/check_bits_3.f90: New test.