[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/shader_recompiler/CMakeLists.txt

@@ -253,7 +253,7 @@ if (MSVC)
     )
 else()
     target_compile_options(shader_recompiler PRIVATE
-        $<$<COMPILE_LANGUAGE:C,CXX>:-Werror=conversion>
+        $<$<COMPILE_LANGUAGE:C,CXX>:-Wconversion>
         # Bracket depth determines maximum size of a fold expression in Clang since 9c9974c3ccb6.
         # And this in turns limits the size of a std::array.
         $<$<CXX_COMPILER_ID:Clang>:-fbracket-depth=1024>