[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/video_core/host_shaders/CMakeLists.txt

@@ -88,7 +88,7 @@ set(SHADER_FILES
     ${CMAKE_CURRENT_SOURCE_DIR}/sgsr1_shader_mobile_edge_direction.frag
 )
 
-if (PLATFORM_HAIKU)
+if (HAIKUOS)
     # glslangValidator WILL crash, glslang will not
     set(GLSLANGVALIDATOR "glslang")
 else()