[cmake, core] Unbreak FreeBSD Building Process (#117)

During building eden on FreeBSD, it always assumed that FreeBSD due to being part of the unix family, has gamemode support, too.
Since it doesn't the building process failed.
This commit aims to fix that by separating out Unix and Linux for CMake to ensure there are no conflicts.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/117
Co-authored-by: SDK-Chan <sdkchan@eden-emu.dev>
Co-committed-by: SDK-Chan <sdkchan@eden-emu.dev>

src/yuzu_cmd/yuzu.cpp

@@ -68,7 +68,7 @@ __declspec(dllexport) int AmdPowerXpressRequestHighPerformance = 1;
 }
 #endif
 
-#ifdef __unix__
+#ifdef __linux__
 #include "common/linux/gamemode.h"
 #endif
 
@@ -410,9 +410,7 @@ int main(int argc, char** argv) {
                          "While attempting to load the ROM requested, an error occurred. Please "
                          "refer to the Eden wiki for more information or the Eden discord for "
                          "additional help.\n\nError Code: {:04X}-{:04X}\nError Description: {}",
-                         loader_id,
-                         error_id,
-                         static_cast<Loader::ResultStatus>(error_id));
+                         loader_id, error_id, static_cast<Loader::ResultStatus>(error_id));
         }
         break;
     }
@@ -447,7 +445,7 @@ int main(int argc, char** argv) {
         exit(0);
     });
 
-#ifdef __unix__
+#ifdef __linux__
     Common::Linux::StartGamemode();
 #endif
 
@@ -462,7 +460,7 @@ int main(int argc, char** argv) {
     void(system.Pause());
     system.ShutdownMainProcess();
 
-#ifdef __unix__
+#ifdef __linux__
     Common::Linux::StopGamemode();
 #endif