libretro: Only offer "Cache Full ISO in RAM" where it works

The option is left out of the core options on mobile, Switch, UWP and
32-bit builds, where the cache isn't used. One macro decides both.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libretro/libretro.cpp

@@ -2101,8 +2101,7 @@ bool System_GetPropertyBool(SystemProperty prop) {
       return true;
 #endif
    case SYSPROP_ENOUGH_RAM_FOR_FULL_ISO:
-      // Desktops only, like the standalone app.
-#if PPSSPP_ARCH(64BIT) && !PPSSPP_PLATFORM(ANDROID) && !PPSSPP_PLATFORM(IOS) && !PPSSPP_PLATFORM(SWITCH) && !PPSSPP_PLATFORM(UWP)
+#ifdef LIBRETRO_CAN_CACHE_ISO_IN_RAM
       return true;
 #else
       return false;

libretro/libretro_core_options.h

@@ -7,6 +7,13 @@
 #include <libretro.h>
 #include <retro_inline.h>
 
+#include "ppsspp_config.h"
+
+// Desktops only, like the standalone app (SYSPROP_ENOUGH_RAM_FOR_FULL_ISO).
+#if PPSSPP_ARCH(64BIT) && !PPSSPP_PLATFORM(ANDROID) && !PPSSPP_PLATFORM(IOS) && !PPSSPP_PLATFORM(SWITCH) && !PPSSPP_PLATFORM(UWP)
+#define LIBRETRO_CAN_CACHE_ISO_IN_RAM 1
+#endif
+
 #ifndef HAVE_NO_LANGEXTRA
 #include "libretro_core_options_intl.h"
 #endif
@@ -223,6 +230,7 @@ struct retro_core_option_v2_definition option_defs_us[] = {
       BOOL_OPTIONS,
       "enabled"
    },
+#ifdef LIBRETRO_CAN_CACHE_ISO_IN_RAM
    {
       "ppsspp_cache_iso",
       "Cache Full ISO in RAM",
@@ -233,6 +241,7 @@ struct retro_core_option_v2_definition option_defs_us[] = {
       BOOL_OPTIONS,
       "disabled"
    },
+#endif
    {
       "ppsspp_cheats",
       "Internal Cheats Support",