On x86_64, openlibm_fenv.h is silently coupled to openlibm_complex.h due to the inclusion of math_private.h inside of openlibm_fenv_amd64.h. The math_private.h header was included to gain access to the OLM_DLLEXPORT macro. However, this macro is redefined, since it is originally defined in openlibm_math.h. This inclusion also exposes math_private.h to public clients, which is undesirable.
Instead, a standalone header is created to contain the OLM_DLLEXPORT definition. This header is used included in the appropriate files. openlibm_fenv_amd64.h is no longer coupled to math_private.h.
