[libc] Mark fixed point type generic macros as complete (#130805)

These were added in #129371.

Author: PiJoules

libc/docs/headers/stdfix.rst

@@ -1,6 +1,6 @@
-================
-StdFix Functions
-================
+========
+stdfix.h
+========
 
 .. include:: ../check.rst
 
@@ -89,9 +89,9 @@ The following functions are included in the ISO/IEC TR 18037:2008 standard.
 ================== =========
 Type Generic Macro Available
 ================== =========
-absfx
-countlsfx
-roundfx
+absfx              |check|
+countlsfx          |check|
+roundfx            |check|
 ================== =========