SDL_power.c: Adjust SDL_POWER_DISABLED ifdefs to avoid zero-size array

Otherwise if SDL_POWER_DISABLED is disabled (eg with --disable-power):

... with clang -pedantic:
src/power/SDL_power.c:48:50: warning: use of GNU empty initializer extension [-Wgnu-empty-initializer]
static SDL_GetPowerInfo_Impl implementations[] = {
                                                 ^
src/power/SDL_power.c:48:50: warning: zero size arrays are an extension [-Wzero-length-array]
2 warnings generated.

... with gcc -pedantic:
src/power/SDL_power.c:48:50: warning: ISO C forbids empty initializer braces [-Wpedantic]
src/power/SDL_power.c:48:50: warning: ISO C forbids empty initializer braces [-Wpedantic]
 static SDL_GetPowerInfo_Impl implementations[] = {
                                                  ^
src/power/SDL_power.c:48:30: error: zero or negative size array ?implementations?
 static SDL_GetPowerInfo_Impl implementations[] = {
                              ^~~~~~~~~~~~~~~

... with Watcom:
./src/power/SDL_power.c(85): Error! E1112: Initializer list cannot be empty

OWMakefile.os2

@@ -19,15 +19,6 @@ CFLAGS+= $(INCPATH)
 # building SDL itself:
 CFLAGS+= -DBUILD_SDL
 
-# this is so that build doesn't fail with E1112:
-#CFLAGS+= -DSDL_POWER_DISABLED
-CFLAGS+= -DSDL_POWER_HARDWIRED
-
-.extensions:
-.extensions: .lib .dll .obj .c .asm
-
-.c: ./src;./src/dynapi;./src/audio;./src/cpuinfo;./src/events;./src/file;./src/haptic;./src/joystick;./src/power;./src/render;./src/render/software;./src/sensor;./src/stdlib;./src/thread;./src/timer;./src/video;./src/video/yuv2rgb;./src/haptic/dummy;./src/joystick/dummy;./src/loadso/dummy;./src/filesystem/dummy;./src/thread/generic;./src/timer/dummy;./src/power;./src/power/os2;./src/atomic;./src/audio/dummy;./src/audio/disk;./src/video/dummy;./src/sensor/dummy;./src/test;
-
 SRCS = SDL.c SDL_assert.c SDL_error.c SDL_log.c SDL_dataqueue.c SDL_hints.c
 SRCS+= SDL_getenv.c SDL_iconv.c SDL_malloc.c SDL_qsort.c SDL_stdlib.c SDL_string.c
 SRCS+= SDL_cpuinfo.c SDL_atomic.c SDL_spinlock.c SDL_thread.c SDL_timer.c
@@ -58,6 +49,11 @@ SRCS+= SDL_dynapi.c
 
 OBJS = $(SRCS:.c=.obj)
 
+.extensions:
+.extensions: .lib .dll .obj .c .asm
+
+.c: ./src;./src/dynapi;./src/audio;./src/cpuinfo;./src/events;./src/file;./src/haptic;./src/joystick;./src/power;./src/render;./src/render/software;./src/sensor;./src/stdlib;./src/thread;./src/timer;./src/video;./src/video/yuv2rgb;./src/haptic/dummy;./src/joystick/dummy;./src/loadso/dummy;./src/filesystem/dummy;./src/thread/generic;./src/timer/dummy;./src/power;./src/power/os2;./src/atomic;./src/audio/dummy;./src/audio/disk;./src/video/dummy;./src/sensor/dummy;./src/test;
+
 all: $(DLLFILE) $(LIBFILE) .symbolic
 
 $(DLLFILE): $(OBJS) $(LNKFILE)

include/SDL_config_os2.h

@@ -28,6 +28,7 @@
 #define SDL_AUDIO_DRIVER_DUMMY 1
 #define SDL_AUDIO_DRIVER_DISK 1
 
+#define SDL_POWER_DISABLED  1
 #define SDL_JOYSTICK_DISABLED 1
 #define SDL_HAPTIC_DISABLED 1
 /*#undef SDL_JOYSTICK_HIDAPI */

src/power/SDL_power.c

@@ -42,11 +42,8 @@ SDL_GetPowerInfo_Hardwired(SDL_PowerState * state, int *seconds, int *percent)
     return SDL_TRUE;
 }
 #endif
-#endif
-
 
 static SDL_GetPowerInfo_Impl implementations[] = {
-#ifndef SDL_POWER_DISABLED
 #ifdef SDL_POWER_LINUX          /* in order of preference. More than could work. */
     SDL_GetPowerInfo_Linux_org_freedesktop_upower,
     SDL_GetPowerInfo_Linux_sys_class_power_supply,
@@ -81,31 +78,34 @@ static SDL_GetPowerInfo_Impl implementations[] = {
 #ifdef SDL_POWER_HARDWIRED
     SDL_GetPowerInfo_Hardwired,
 #endif
-#endif
 };
+#endif
 
 SDL_PowerState
 SDL_GetPowerInfo(int *seconds, int *percent)
 {
+#ifndef SDL_POWER_DISABLED
     const int total = sizeof(implementations) / sizeof(implementations[0]);
-    int _seconds, _percent;
     SDL_PowerState retval = SDL_POWERSTATE_UNKNOWN;
     int i;
+#endif
 
+    int _seconds, _percent;
     /* Make these never NULL for platform-specific implementations. */
     if (seconds == NULL) {
         seconds = &_seconds;
     }
-
     if (percent == NULL) {
         percent = &_percent;
     }
 
+#ifndef SDL_POWER_DISABLED
     for (i = 0; i < total; i++) {
         if (implementations[i](&retval, seconds, percent)) {
             return retval;
         }
     }
+#endif
 
     /* nothing was definitive. */
     *seconds = -1;