[libc] Support the `abs` functions in the GPU libc.

[jhuber6]

Summary

This patch simply enables building the integer abs functions for the
GPU.

[jhuber6]

This is the first set of functions that may shadow some of the definitions that the GPU header wrappers provide.

[sivachandra]

libc/config/gpu/api.td

13

Why are these types required?

[jhuber6]

libc/config/gpu/api.td

13

It didn't build, and the div_t stuff is simply a struct of integers. I could make this patch provide div as well since it's relatively simple.

[jhuber6]

Remove ldiv types

libc/config/gpu/api.td

 include "config/public_api.td"
 
 include "spec/stdc.td"
 
 def StringAPI : PublicAPI<"string.h"> {
   let Types = ["size_t"];
 }
 
 def StdlibAPI : PublicAPI<"stdlib.h"> {
   let Types = [
+    "div_t",
+    "ldiv_t",
+    "lldiv_t",
     "size_t",
     "__atexithandler_t",
   ];
 }
 
 def FenvAPI: PublicAPI<"fenv.h"> {
   let Types = ["fenv_t"];
 }

libc/config/gpu/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.strpbrk
     libc.src.string.strrchr
     libc.src.string.strspn
     libc.src.string.strstr
     libc.src.string.strtok
     libc.src.string.strtok_r
 
     # stdlib.h entrypoints
+    libc.src.stdlib.abs
     libc.src.stdlib.atoi
     libc.src.stdlib.atof
     libc.src.stdlib.atol
     libc.src.stdlib.atoll
+    libc.src.stdlib.labs
+    libc.src.stdlib.llabs
     libc.src.stdlib.atexit
     libc.src.stdlib.strtod
     libc.src.stdlib.strtof
     libc.src.stdlib.strtol
     libc.src.stdlib.strtold
     libc.src.stdlib.strtoll
     libc.src.stdlib.strtoul
     libc.src.stdlib.strtoull

libc/docs/gpu/support.rst

 =============  =========  ============
 
 stdlib.h
 --------
 
 =============  =========  ============
 Function Name  Available  RPC Required
 =============  =========  ============
+abs            |check|
 atoi           |check|
 atof           |check|
 atol           |check|
 atoll          |check|
 atexit         |check|
+labs           |check|
+llabs          |check|
 strtod         |check|
 strtof         |check|
 strtol         |check|
 strtold        |check|
 strtoll        |check|
 strtoul        |check|
 strtoull       |check|
 =============  =========  ============