getopt varies too much between platforms, and we already use compat/getopt.c

for Linux so just use it everywhere.

configure.ac

@@ -125,6 +125,12 @@ AC_FUNC_STRNLEN
 # Look for clock_gettime. Must come before event_init.
 AC_SEARCH_LIBS(clock_gettime, rt)
 
+# Always use our getopt because 1) glibc's doesn't enforce argument order 2)
+# musl does not set optarg to NULL for flags without arguments (although it is
+# not required to, but it is helpful) 3) there are probably other weird
+# implementations.
+AC_LIBOBJ(getopt)
+
 # Look for libevent.
 PKG_CHECK_MODULES(
 	LIBEVENT,
@@ -424,40 +430,6 @@ else
 	AC_LIBOBJ(unvis)
 fi
 
-# Look for getopt. glibc's getopt does not enforce argument order and the ways
-# of making it do so are stupid, so just use our own instead.
-AC_CHECK_FUNC(getopt, found_getopt=yes, found_getopt=no)
-if test "x$found_getopt" != xno; then
-	AC_MSG_CHECKING(if getopt is suitable)
-	AC_EGREP_CPP(
-		yes,
-		[
-			#include <features.h>
-			#ifdef __GLIBC__
-			yes
-			#endif
-		],
-		[
-			found_getopt=no
-			AC_MSG_RESULT(no)
-		],
-		AC_MSG_RESULT(yes))
-fi
-if test "x$found_getopt" != xno; then
-	AC_CHECK_DECLS(
-		[optarg, optind, optreset],
-		,
-		found_getopt=no,
-		[
-			#include <unistd.h>
-		])
-fi
-if test "x$found_getopt" != xno; then
-	AC_DEFINE(HAVE_GETOPT)
-else
-	AC_LIBOBJ(getopt)
-fi
-
 # Look for fdforkpty and forkpty in libutil.
 AC_SEARCH_LIBS(fdforkpty, util, found_fdforkpty=yes, found_fdforkpty=no)
 if test "x$found_fdforkpty" = xyes; then