[libc] Disable varargs tests on gpu, nvptx can't build them yet

Author: JonChesterfield

libc/config/gpu/entrypoints.txt

@@ -181,10 +181,6 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.fflush
     libc.src.stdio.ftell
     libc.src.stdio.clearerr
-    libc.src.stdio.sprintf
-    libc.src.stdio.snprintf
-    libc.src.stdio.vsprintf
-    libc.src.stdio.vsnprintf
     libc.src.stdio.puts
     libc.src.stdio.fopen
     libc.src.stdio.fclose

libc/test/src/__support/CMakeLists.txt

@@ -86,8 +86,8 @@ add_libc_test(
     libc.src.__support.uint128
 )
 
-# NVPTX does not support varargs currently.
-if(NOT LIBC_TARGET_ARCHITECTURE_IS_NVPTX)
+# The GPU does not support varargs currently.
+if(NOT LIBC_TARGET_OS_IS_GPU)
   add_libc_test(
     arg_list_test
     SUITE