std-aux: drop assertion and function name from assert() in release mode

For g_assert() and g_return*() we already do the same, in
"src/libnm-glib-aux/nm-gassert-patch.h"

Also patch __assert_fail() so that it omits the condition text and the
function name in production builds.

Note that this is a bit ugly, for two reasons:

- again, we make assumptions that __assert_fail() exists. In practice,
  this is the case for glibc and musl.

- <assert.h> can be included multiple times, while also forward
  declaring __assert_fail(). That means, we cannot add a macro

  #define __assert_fail(...)

  because that would break the forward declaration. Instead,
  just `#define __assert_fail _nm_assert_fail_internal`

Of course, this only affects direct calls to assert(), which we have
few. nm_assert() is not affected, because that anyway doesn't do
anything, unless NM_MORE_ASSERTS is enabled.

src/libnm-glib-aux/tests/test-shared-general.c

@@ -78,6 +78,9 @@ test_gpid(void)
      * the case. */
     int_ptr = &pid;
     g_assert_cmpint(*int_ptr, ==, 42);
+
+    /* also check how assert() works. */
+    assert(*int_ptr == 42);
 }
 
 /*****************************************************************************/

src/libnm-std-aux/nm-std-aux.h

@@ -194,6 +194,25 @@ typedef uint64_t _nm_bitwise nm_be64_t;
 #define NM_MORE_ASSERTS 0
 #endif
 
+#if NM_MORE_ASSERTS == 0
+/* The string with the assertion check and the function name blows up the
+ * binary size. In production mode, let's drop those, similar to
+ * g_assertion_message_expr.
+ *
+ * Note that <assert.h> can be included multiple times. We can thus
+ * not redefine __assert_fail(...). Instead, just redefine the name
+ * __assert_fail. */
+_nm_noreturn static inline void
+_nm_assert_fail_internal(const char  *assertion,
+                         const char  *file,
+                         unsigned int line,
+                         const char  *function)
+{
+    __assert_fail("<dropped>", file, line, "<unknown-fcn>");
+}
+#define __assert_fail _nm_assert_fail_internal
+#endif
+
 #define _nm_assert_fail(msg) __assert_fail((msg), __FILE__, __LINE__, __func__)
 #ifndef NDEBUG
 #define _NM_ASSERT_FAIL_ENABLED 1