selftests/bpf: impose global ordering for test decl_tags

selftests/bpf: impose global ordering for test decl_tags

Impose global ordering for all decl tags used by test_loader.c based
tests (__success, __failure, __msg, etc):
- change every tag to expand as
  __attribute__((btf_decl_tag("comment:" XSTR(__COUNTER__) ...)))
- change parse_test_spec() to collect all decl tags before
  processing and sort them using strverscmp().

The ordering is necessary for gcc-bpf.
Neither GCC nor the C standard defines the order in which function
attributes are consumed. While Clang tends to preserve definition order,
GCC may process them out of sequence. This inconsistency causes BPF
tests with multiple __msg entries to fail when compiled with GCC.

Signed-off-by: Cupertino Miranda <cupertino.miranda@oracle.com>
Reviewed-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260410-selftests-global-tags-ordering-v2-3-c566ec9781bf@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>