tests: extend coverage of execve and execveat syscalls

tests: extend coverage of execve and execveat syscalls

Check decoding of inaccessible or partially inaccessible arrays.

* tests/execve-v.c: New file.
* tests/execveat-v.c: Likewise.
* tests/execve-v.test: New test.
* tests/execveat-v.test: Likewise.
* tests/execve.c: Rewrite.
* tests/execveat.c: Likewise.
* tests/execve.test: Likewise.
* tests/execveat.test: Likewise.
* tests/execve.expected: Remove.
* tests/execve-v.expected: Likewise.
* tests/execveat.expected: Likewise.
* tests/execveat-v.expected: Likewise.
* tests/.gitignore: Add execve-v and execveat-v.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(TESTS): Add execve-v.test and execveat-v.test.
(EXTRA_DIST): Remove execve.expected, execve-v.expected,
execveat.expected, and execveat-v.expected.