selftests/sched_ext: Add -fms-extensions to bpf build flags

Similar to commit 835a507 ("selftests/bpf: Add -fms-extensions to
bpf build flags") and commit 639f58a ("bpftool: Fix build warnings
due to MS extensions")

Fix "declaration does not declare anything" warning by using
-fms-extensions and -Wno-microsoft-anon-tag flags to build bpf programs
that #include "vmlinux.h"

Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: Zhao Mengmeng

tools/testing/selftests/sched_ext/Makefile

@@ -93,6 +93,8 @@ BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH)					\
 	     $(CLANG_SYS_INCLUDES) 						\
 	     -Wall -Wno-compare-distinct-pointer-types				\
 	     -Wno-incompatible-function-pointer-types				\
+	     -Wno-microsoft-anon-tag						\
+	     -fms-extensions							\
 	     -O2 -mcpu=v3
 
 # sort removes libbpf duplicates when not cross-building