Use system getopt instead of local copy

https://bugs.gentoo.org/895882
https://bugs.gentoo.org/944257

--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,5 +1,5 @@
 bin_PROGRAMS = awale
-awale_SOURCES = awale.c getopt.c getopt1.c getopt.h
+awale_SOURCES = awale.c
 INCLUDES = -I. -I$(srcdir)
 bin_SCRIPTS = xawale
 xawale: