[cmake] Simplify DetectPlatform and normalize platform names (#4183)

Since 3.25 introduced `LINUX` and `BSD`, use them, and standardize other platforms to that style

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4183
Reviewed-by: Samuel <lizzie@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

src/core/CMakeLists.txt

@@ -1173,7 +1173,7 @@ add_library(core STATIC
 
 if (ENABLE_WIFI_SCAN)
     target_sources(core PRIVATE internal_network/wifi_scanner.cpp)
-    if (PLATFORM_LINUX)
+    if (LINUX)
         target_link_libraries(core PRIVATE iw)
     endif()
 else()