tests: libc: Update libc testcases to solve coverity issues

1. Refine some testcases for testing some libc functions, include
strlen(),strcmp(),strncmp(),memcmp(),memstr(),memcpy(),memmove()
strtol(),strtoul().
2. Change some code to make the code style consistent.

Fixes #33794
Fixes #33810
Fixes #33806

Signed-off-by: Ying ming <[email protected]>