[libc] Enable 'sscanf' on the GPU (#100211)

Summary:
We can enable the `sscanf` function on the GPU now.

Author: jhuber6

libc/config/gpu/entrypoints.txt

@@ -186,6 +186,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.sprintf
     libc.src.stdio.vsnprintf
     libc.src.stdio.vsprintf
+    libc.src.stdio.sscanf
     libc.src.stdio.feof
     libc.src.stdio.ferror
     libc.src.stdio.fflush

libc/docs/gpu/support.rst

@@ -234,10 +234,11 @@ printf         |check|    |check|
 vprintf        |check|    |check|
 fprintf        |check|    |check|
 vfprintf       |check|    |check|
-sprintf        |check|    |check|
-snprintf       |check|    |check|
-vsprintf       |check|    |check|
-vsnprintf      |check|    |check|
+sprintf        |check|
+snprintf       |check|
+vsprintf       |check|
+vsnprintf      |check|
+sscanf         |check|
 putchar        |check|    |check|
 fclose         |check|    |check|
 fopen          |check|    |check|