selftests/bpf: Add exception tests with stack arguments

selftests/bpf: Add exception tests with stack arguments

Add tests to verify that bpf_throw() correctly unwinds the stack
when the program uses outgoing stack arguments (functions with >5
args). Without the preceding x86 fix, these tests crash the kernel
on x86 due to corrupted callee-saved register restore. There is
no change for arm64 to support exception with stack arguments.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260517150707.289273-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>