Add NO_CHECK_OBJ macro to neuter CHECK_OBJ

[nigoroll]

The CHECK_OBJ*() macros are great, and no-one could ever want to live without them, but they have one disadvantage: They prevent compiler warnings about unused variables.

So, for this purpose only, we add NO_CHECK_OBJ to discover more unused variables:

$ make CFLAGS='-DNO_CHECK_OBJ -Wall -Werror'
...
cache/cache_gzip.c:420:17: error: variable 'wrk' set but not used [-Werror,-Wunused-but-set-variable]
        struct worker *wrk;

[asadsa92]

Nice, maybe controversial, but did you try to omit asserts, AN(), AZ(), etc., to see if we got some dead code only accessed by our defensive code style? I.e.,

$ make CFLAGS="-DNDEBUG -Wall -Werror"
[...]
vbm_test.c:46:16: error: variable 'obits' set but not used [-Werror,-Wunused-but-set-variable]
        VBITMAP_TYPE    *obits;
                         ^

[nigoroll]

@asadsa92 -DNDEBUG and -DWITHOUT_ASSERTS are other options to maybe check periodically, yes.

bugwash was -1 on merging this, but we might want to polish the CHECK_OBJ()s to make the intention clear.