[libc] Disable block test on AMDGPU as well

Summary:
Recently started failing on AMDGPU as well, will disable until I can
bisect it.

Author: jhuber6

libc/test/src/__support/CMakeLists.txt

@@ -1,6 +1,6 @@
 add_custom_target(libc-support-tests)
 
-if(NOT LIBC_TARGET_ARCHITECTURE_IS_NVPTX)
+if(NOT LIBC_TARGET_OS_IS_GPU)
   add_libc_test(
     block_test
     SUITE