syscalls: add selftest for execveat(2)

syscalls: add selftest for execveat(2)

Signed-off-by: David Drysdale <[email protected]>
Cc: Meredydd Luff <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>