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.

hyperweb.cpp

@@ -30,10 +30,6 @@
 #define EMSCRIPTEN
 #endif
 
-#ifndef CAP_ORIENTATION
-#define CAP_ORIENTATION 1
-#endif
-
 #ifdef FAKEWEB
 namespace hr { void mainloopiter(); }
 template<class A, class B, class C> void emscripten_set_main_loop(A a, B b, C c) { while(true) mainloopiter(); }