[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/dynarmic/CMakeLists.txt

@@ -25,7 +25,7 @@ endif()
 # Dynarmic project options
 option(DYNARMIC_ENABLE_CPU_FEATURE_DETECTION "Turning this off causes dynarmic to assume the host CPU doesn't support anything later than SSE3" ON)
 
-if (PLATFORM_OPENBSD OR PLATFORM_DRAGONFLY OR PLATFORM_NETBSD)
+if (OPENBSD OR DRAGONFLY OR NETBSD)
     set(REQUIRE_WX ON)
 else()
     set(REQUIRE_WX OFF)

src/dynarmic/src/dynarmic/CMakeLists.txt

@@ -363,7 +363,7 @@ elseif (APPLE)
             backend/exception_handler_macos_mig.c
         )
     endif()
-elseif (UNIX AND NOT PLATFORM_HAIKU)
+elseif (UNIX AND NOT HAIKUOS)
     # Haiku lacks <ucontext.h>
     if (CMAKE_SYSTEM_NAME STREQUAL "Linux")
         target_link_libraries(dynarmic PRIVATE rt)