macros: define NM_MORE_ASSERTS is not defined

In NetworkManager's configure script we have --with-more-asserts
option which always defines NM_MORE_ASSERTS in config.h.

When reusing the header file outside of NetworkManager, the
NM_MORE_ASSERTS define might be unset. Define it in that case
to avoid compiler warnings about undefined preprocessor define.

shared/nm-macros-internal.h

@@ -297,6 +297,22 @@ _NM_IN_STRSET_streq (const char *x, const char *s)
 
 /*****************************************************************************/
 
+/* glib/C provides the following kind of assertions:
+ *   - assert() -- disable with NDEBUG
+ *   - g_return_if_fail() -- disable with G_DISABLE_CHECKS
+ *   - g_assert() -- disable with G_DISABLE_ASSERT
+ * but they are all enabled by default and usually even production builds have
+ * these kind of assertions enabled. It also means, that disabling assertions
+ * is an untested configuration, and might have bugs.
+ *
+ * Add our own assertion macro nm_assert(), which is disabled by default and must
+ * be explicitly enabled. They are useful for more expensive checks or checks that
+ * depend less on runtime conditions (that is, are generally expected to be true). */
+
+#ifndef NM_MORE_ASSERTS
+#define NM_MORE_ASSERTS 0
+#endif
+
 #if NM_MORE_ASSERTS
 #define nm_assert(cond) G_STMT_START { g_assert (cond); } G_STMT_END
 #define nm_assert_not_reached() G_STMT_START { g_assert_not_reached (); } G_STMT_END