[*] basic in-house cpp linting (#4039)

- add `#pragma once` to remainder files
- "correcter" defines (ANDROID), see https://groups.google.com/g/android-ndk/c/cf9_f1SLXls
- extra miscelly fixups

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4039
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: crueter <crueter@eden-emu.dev>

src/frontend_common/firmware_manager.cpp

@@ -13,7 +13,7 @@
 #include "core/crypto/key_manager.h"
 #include "frontend_common/content_manager.h"
 
-#ifdef ANDROID
+#ifdef __ANDROID__
 #include <jni.h>
 #include <common/android/id_cache.h>
 #include <common/android/android_common.h>
@@ -25,7 +25,7 @@ FirmwareManager::InstallKeys(std::string location, std::string extension) {
 
     const auto keys_dir = Common::FS::GetEdenPath(Common::FS::EdenPath::KeysDir);
 
-#ifdef ANDROID
+#ifdef __ANDROID__
     JNIEnv *env = Common::Android::GetEnvForThread();
 
     jstring jsrc = Common::Android::ToJString(env, location);