Use consistent syntax for boolean preprocessor expressions.

src/c_screen.cpp

@@ -28,7 +28,7 @@
 
 #include "conf.h"
 
-#if defined(USE_SCREEN)
+#if (USE_SCREEN)
 
 #include "screen.h"
 
@@ -130,15 +130,15 @@ static int init(FILE *f, int o, int now)
     if (!screen)
         screen = do_construct(screen_djgpp2_construct(),fd);
 #endif
-#if defined(USE_SCREEN_WIN32)
+#if (USE_SCREEN_WIN32)
     if (!screen)
         screen = do_construct(screen_win32_construct(),fd);
 #endif
-#if defined(USE_SCREEN_VCSA)
+#if (USE_SCREEN_VCSA)
     if (!screen)
         screen = do_construct(screen_vcsa_construct(),fd);
 #endif
-#if defined(USE_SCREEN_CURSES)
+#if (USE_SCREEN_CURSES)
     if (!screen && o == CON_SCREEN)
         screen = do_construct(screen_curses_construct(),fd);
 #endif
@@ -298,7 +298,7 @@ static void print0(FILE *f, const char *ss)
 static bool intro(FILE *f)
 {
     UNUSED(f);
-#if defined(USE_FRAMES)
+#if (USE_FRAMES)
     if (screen->intro)
         return screen->intro(screen,screen_show_frames);
 #endif