Move all defaulting-of-CAP_FOO to sysconfig.h.

- The phrase `#ifdef CAP_` should never appear anywhere.

- The phrase `#ifndef CAP_` should appear only in sysconfig.h.

- The phrases `#if CAP_` and `#if !CAP_` may appear wherever,
    as long as "sysconfig.h" is included first.

The rules for `CAP_FOO` equally apply to `ISFOO`.

There are many one-off macros still tested with `#ifdef`,
including `HAVE_ACHIEVEMENTS`, `PRINT_ACHIEVEMENTS`,
`FAKEWEB`, `FAKE_SDL`, `EASY`, and `WHATEVER`. I don't
have much grasp on what these are used for or how they're
configured, so I'm leaving them alone.

inventory.cpp

@@ -588,7 +588,7 @@ EX namespace inv {
           displaystr(vid.xres/2, vid.yres - vid.fsize*6, 2, vid.fsize, osminfo(which), icol, 8);
           }
 
-#if ISMOBILE==0
+#if !ISMOBILE
         string hot = XLAT1("Hotkey: "); hot += getcstat;
         displaystr(vid.xres/2, vid.yres - vid.fsize*5, 2, vid.fsize, hot, icol, 8);
 #endif