[flang][NFC] document BOZ error in DIM, MOD, MODULO, and SIGN (#87779)

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 |