fix -Wpedantic warnings

[bratpiorka]

fix -Wpedantic warnings

	In file included from /home/rrudnick/llvm/build_sycl/_deps/unified-memory-framework-src/src/memory_pool.c:19:
	/home/rrudnick/llvm/build_sycl/_deps/unified-memory-framework-src/src/ctl/ctl_internal.h:168:43: warning: initialization of a flexible array member [-Wpedantic]
	  168 |         sizeof(void *), CTL_ARG_TYPE_PTR, { {0, 0, NULL}, CTL_ARG_PARSER_END } \
	      |                                           ^
	      |                                                       ^~~~~~~~~~~

and

	[38/1059] Building C object _deps/unified-memory-framework-build/src/CMakeFiles/umf.dir/pool/pool_disjoint.c.o
	/home/rrudnick/llvm/build_sycl/_deps/unified-memory-framework-src/src/pool/pool_disjoint.c:30:29: warning: initialization discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
	   30 | static char *DEFAULT_NAME = "disjoint";

[lukaszstolarczuk]

LGTM