[cmake] Add ENABLE_WERROR option (#4080)

Should warnings be errors? that's a philosophical debate which I can only answer with "no, but if you think otherwise here is an option for you"

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

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4080
Reviewed-by: crueter <crueter@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

src/input_common/CMakeLists.txt

@@ -44,7 +44,7 @@ if (MSVC)
         /we4800 # Implicit conversion from 'type' to bool. Possible information loss
     )
 else()
-    target_compile_options(input_common PRIVATE $<$<COMPILE_LANGUAGE:C,CXX>:-Werror=conversion>)
+    target_compile_options(input_common PRIVATE $<$<COMPILE_LANGUAGE:C,CXX>:-Wconversion>)
 endif()
 
 if (ANDROID)