what is intended to be dllexport-ed?

When I went through openlibm_fenv_i387.h and added `OLM_DLLEXPORT`, it felt like the `__has_sse`/`__test_sse` symbols should have been private, but they were used by the tests so had to be exported.

Looking through other headers, I see openlibm_fenv_amd64.h is better about having `OLM_DLLEXPORT`, but I notice it is missing from `__fe_dfl_env`. It seems that this would need to be exported for `FE_DFL_ENV` macro to work. Probably also need to be done in the arm.h as well.

openlibm_complex.h has *no* `OLM_DLLEXPORT` annotations. I assume this is intended to be a public API, yes?

There is some hackery for amd64 with regard to exporting inline functions. This hackery does not seem to be present for i387 or aarch64. I am not sure what precise problem it is intended to solve, but it seems like if it's necessary for amd64 it would be necessary for all.