[flang][NFC] document BOZ error in DIM, MOD, MODULO, and SIGN

[jeanPerier]

It is highly ambiguous to what type BOZ should be resolved in DIM, MOD, MODULO, and SIGN intrinsic arguments. Some other compilers accept them, but none agree. See table below.

List them explicitly as non supported extensions (semantics already reject them, this is an NFC).

Table listing the resolved types of the intrinsic results when there is a BOZ argument:

	gfortran	nvfortran	ifort	nagfor	xlf
DIM(INT4, BOZ)	INT16	INT4	INT8	crash	INT4
DIM(BOZ, REAL4)	error	INT8	error	error	REAL4
DIM(REAL4, BOZ)	error	REAL4	error	error	REAL4
DIM(BOZ, INT4)	INT16	INT8	INT8	INT8	INT4
DIM(BOZ, BOZ)	INT16	INT8	INT8	INT8	REAL4
MOD(INT4, BOZ)	INT16	INT4	INT8	crash	INT4
MOD(BOZ, REAL4)	error	INT8	error	error	REAL4
MOD(REAL4, BOZ)	error	REAL4	error	error	REAL4
MOD(BOZ, INT4)	INT16	INT8	INT8	INT8	INT4
MOD(BOZ, BOZ)	INT16	INT8	INT8	INT8	INT4
MODULO(INT4, BOZ)	INT16	INT4	INT8	crash	INT4
MODULO(BOZ, REAL4)	error	INT8	error	error	REAL4
MODULO(REAL4, BOZ)	error	REAL4	error	error	REAL4
MODULO(BOZ, INT4)	INT16	INT8	INT8	INT8	INT4
MODULO(BOZ, BOZ)	INT16	INT8	INT8	INT8	INT8
SIGN(INT4, BOZ)	error	INT4	INT8	INT4	INT4
SIGN(BOZ, REAL4)	error	INT8	error	error	REAL4
SIGN(REAL4, BOZ)	error	REAL4	error	error	REAL4
SIGN(BOZ, INT4)	error	INT8	INT8	INT8	INT4
SIGN(BOZ, BOZ)	INT16	INT8	INT8	INT8	REAL4

[psteinfeld]

Looks great!