arch: Avoid explicit access to 'environ'

We pass 'environ' to execve() in arch_avc2_exec(), so that we retain the
environment in the current process.  But the declaration of 'environ' is
a bit weird - it doesn't seem to be in a standard header, requiring a
manual explicit declaration.  But, we can avoid needing to reference it
explicitly by using execv() instead of execve().  This removes a clang
warning.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

arch.c

@@ -45,7 +45,7 @@ void arch_avx2_exec(char **argv)
 				   "%s.avx2", exe))
 			die_perror("Can't build AVX2 executable path");
 
-		execve(new_path, argv, environ);
+		execv(new_path, argv);
 		warn_perror("Can't run AVX2 build, using non-AVX2 version");
 	}
 }