Make GameInput c++98 compatible

[madebr]

With a few small changes to lib/GameInput.cpp, it can be made c++98-compatible.
This is useful for SDL to keep compatibility with toolchains that support the standards of the late nineties (c99/c++98).

I verified this change by using the following CMakeLists.txt, and configuring with -DCMAKE_CXX_STANDARD=98.

cmake_minimum_required(VERSION 3.20)
project(GameInput CXX)

if(NOT WIN32)
    message(FATAL_ERROR "Invalid platform")
endif()

add_library(gameinput STATIC lib/GameInput.cpp)
target_compile_definitions(gameinput PRIVATE _UNICODE UNICODE)
if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|IntelLLVM")
    # Avoid a dependency on libstdc++-X.dll for `__gxx_personality_seh0`
    include(CheckCXXCompilerFlag)
    check_cxx_compiler_flag(-fno-exceptions CXX_COMPILER_SUPPORTS_FNO_EXCEPTIONS)
    if(CXX_COMPILER_SUPPORTS_FNO_EXCEPTIONS)
        target_compile_options(gameinput PRIVATE "-fno-exceptions")
    endif()
endif()