[stdfix] Update function names (llvm#129129)

The remaining math functions are `mulifx` (int * fx = int), `divifx`
(int / fx = int), `fxdivi` (int / int = fx), and `idivfx` (fx / fx =
int).

Author: PiJoules

libc/docs/headers/math/stdfix.rst

@@ -75,13 +75,13 @@ The following functions are included in the ISO/IEC TR 18037:2008 standard.
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
 | countls       | |check|        | |check|     | |check|       | |check|    | |check|        | |check|     | |check|        | |check|     | |check|       | |check|    | |check|        | |check|     |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
-| divi          |                |             |               |            |                |             |                |             |               |            |                |             |
+| divi\*        |                |             |               |            |                |             |                |             |               |            |                |             |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
-| idivi         |                |             |               |            |                |             |                |             |               |            |                |             |
+| idiv\*        |                |             |               |            |                |             |                |             |               |            |                |             |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
 | muli          |                |             |               |            |                |             |                |             |               |            |                |             |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
-| rdivi         |                |             |               |            |                |             |                |             |               |            |                |             |
+| \*divi        |                |             |               |            |                |             |                |             |               |            |                |             |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
 | round         | |check|        | |check|     | |check|       | |check|    | |check|        | |check|     | |check|        | |check|     | |check|       | |check|    | |check|        | |check|     |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+