Method Guard

tests/cpu/Caching_tests.cpp:27–31

struct Guard
{
    Guard()
        :    m_envvar(OCIO::OCIO_DISABLE_ALL_CACHES)
    {
        OCIO::Platform::Setenv(m_envvar.c_str(), "1");
    }

    explicit Guard(const char * envvar)
        :    m_envvar(envvar ? envvar : "")