CMake add setuper msvc compiler specific flags
Hello, I have issue with compile glad for MSVC and static runtime library, please add this code for you CMakeLists.txt or similar

```
if (MSVC)
    option(USE_MSVC_RUNTIME_LIBRARY_DLL "Use MSVC runtime library DLL" ON)
endif()

#--------------------------------------------------------------------
# Set compiler specific flags
#--------------------------------------------------------------------
if (MSVC)
    if (NOT USE_MSVC_RUNTIME_LIBRARY_DLL)
        foreach (flag CMAKE_C_FLAGS
                      CMAKE_C_FLAGS_DEBUG
                      CMAKE_C_FLAGS_RELEASE
                      CMAKE_C_FLAGS_MINSIZEREL
                      CMAKE_C_FLAGS_RELWITHDEBINFO)

            if (${flag} MATCHES "/MD")
                string(REGEX REPLACE "/MD" "/MT" ${flag} "${${flag}}")
            endif()
            if (${flag} MATCHES "/MDd")
                string(REGEX REPLACE "/MDd" "/MTd" ${flag} "${${flag}}")
            endif()

        endforeach()
    endif()
endif()
```
get from https://github.com/glfw/glfw/blob/master/CMakeLists.txt