samd: Add support for building with user C modules.

Fixes issue #7545.

Signed-off-by: Damien George <damien@micropython.org>

ports/samd/main.c

@@ -87,6 +87,11 @@ void nlr_jump_fail(void *val) {
     }
 }
 
+void abort(void) {
+    for (;;) {
+    }
+}
+
 #ifndef NDEBUG
 void MP_WEAK __assert_func(const char *file, int line, const char *func, const char *expr) {
     mp_printf(MP_PYTHON_PRINTER, "Assertion '%s' failed, at file %s:%d\n", expr, file, line);