[libc] Enable conversion functions on the GPU

[jhuber6]

Summary

These functions were previously removed due to problems running the
tests with errno in them. This was resolved previously by making the
internal implementation of these functions use a global errno so that
tests can still use errno functionality as long as they are run with a
single thread. This allows us to re-enable these tests as a previous
patch has also resolved the issue where the stdlib tests could not be
hermetic due to the dependence on system rounding functions.

libc/config/gpu/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     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.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
 
     # stdlib.h entrypoints
     libc.src.stdlib._Exit
     libc.src.stdlib.atexit
     libc.src.stdlib.exit
 
     # Only implemented in the test suite
     libc.src.stdlib.malloc

libc/docs/gpu/support.rst

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