Add support for non-glibc systems

MaxScale can now be built on systems that use an alternative libc
implementation e.g. musl.

server/core/maxpasswd.c

@@ -35,6 +35,7 @@
 
 #include "maxscale/secrets.h"
 
+#ifdef HAVE_GLIBC
 struct option options[] =
 {
     {
@@ -45,6 +46,7 @@ struct option options[] =
     },
     { NULL, 0, NULL, 0 }
 };
+#endif
 
 void print_usage(const char* executable, const char* directory)
 {
@@ -107,7 +109,11 @@ int main(int argc, char **argv)
     const char* path = get_datadir();
 
     int c;
+#ifdef HAVE_GLIBC
     while ((c = getopt_long(argc, argv, "h", options, NULL)) != -1)
+#else
+    while ((c = getopt(argc, argv, "h")) != -1)
+#endif
     {
         switch (c)
         {