Add execv() to libc

add symbol for porting CRuby

Signed-off-by: KANATSU Minoru <icc.pot.tyew272@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

libc/process/execv.c

+#include <unistd.h>
+
+extern char **__environ;
+
+int execv(const char *path, char *const argv[])
+{
+	return execve(path, argv, __environ);
+}