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.

complex.cpp

@@ -3848,12 +3848,12 @@ EX namespace halloween {
       }
     int id = hrand(100);
     if(items[itTreat] == 1) {
-#if ISMOBILE==0
+#if !ISMOBILE
       addMessage(XLAT("Hint: use arrow keys to scroll."));
 #endif
       }
     else if(items[itTreat] == 2) {
-#if ISMOBILE==0
+#if !ISMOBILE
       addMessage(XLAT("Hint: press 1 2 3 4 to change the projection."));
 #endif
       }