While building on Mac OS X, this code in src/callproc.c (line 1582ish):

#ifdef HAVE_NS
  if (data_dir == 0)
    data_dir == ns_etc_directory () != 0;
#endif

gives a warning:

cc   -c  -Demacs  -I. -I. -I../lib -I../lib                   -MMD -MF
deps/callproc.d -MP   -Wno-switch
-Wno-tautological-constant-out-of-range-compare -Wno-pointer-sign  -g3
-O2  callproc.c

callproc.c:1582:14: warning: comparison between pointer and integer
('int' and 'const char *')
    data_dir == ns_etc_directory () != 0;
    ~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~
callproc.c:1582:37: warning: inequality comparison result unused
[-Wunused-comparison]
    data_dir == ns_etc_directory () != 0;
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~

2 warnings generated.

Maybe s/==/=/ ?

Looks like it was added in bzr r117829 (the huge alloca() patch).

-David