Stubbed Setuid and friends. Stubbed Exec (#3290)

Co-authored-by: TachyonicBytes <TB>

src/syscall/syscall_linux.go

@@ -0,0 +1,8 @@
+package syscall
+
+func Setuid(code int) (err error)
+func Setgid(code int) (err error)
+func Setreuid(ruid, euid int) (err error)
+func Setregid(rgid, egid int) (err error)
+func Setresuid(ruid, euid, suid int) (err error)
+func Setresgid(rgid, egid, sgid int) (err error)

src/syscall/syscall_unix.go

@@ -0,0 +1,3 @@
+package syscall
+
+func Exec(argv0 string, argv []string, envv []string) (err error)