tests: extend test coverage of getuid/getgid family syscalls

tests: extend test coverage of getuid/getgid family syscalls

Add strict tests for getuid, getuid32, getgid, getgid32, geteuid,
geteuid32, getegid, and getegid32 syscalls.

* tests/getegid.c: New file.
* tests/getegid.test: New test.
* tests/getegid32.c: New file.
* tests/getegid32.test: New test.
* tests/geteuid.c: New file.
* tests/geteuid.test: New test.
* tests/geteuid32.c: New file.
* tests/geteuid32.test: New test.
* tests/getgid.c: New file.
* tests/getgid.test: New test.
* tests/getgid32.c: New file.
* tests/getgid32.test: New test.
* tests/getuid.c: New file.
* tests/getuid.test: New test.
* tests/getuid32.c: New file.
* tests/getuid32.test: New test.
* tests/.gitignore: Add getuid, getuid32, getgid, getgid32, geteuid,
* geteuid32, getegid, and getegid32.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add getegid.test, getegid32.test, geteuid.test,
geteuid32.test, getgid.test, getgid32.test, getuid.test,
and getuid32.test.