[BPF][Clang] Fix func argument pattern in bpf-stack-protector test

Commit 56b038f8("[BPF][clang] Ignore stack protector options for BPF
target") added a test for its corresponding functionality.
Douglas Yung found that the test will fail with the release build
buildbot due to different func argument patterns (from %msg
to %0). This patch fixed the issue by using pattern [0-9a-z]+
which allows both %msg and %0.