Fix some homebrew and osx related errors

[iskra-vitaly]

Fixed these 2 issues:

• loadHDF5Header exception when HDF5_INCLUDE_PATH has more than 1 directory (included /usr/local/opt/szip/include my case)
• "gcc -E" from OSX does not remove '_Nullable' annotation by default – that causes ffi.cdef to throw an exception.

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[iskra-vitaly]

I signed it!

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[iskra-vitaly]

I don't see an option to remove the 'Draft' status from this PR, but I think it may be reviewed already...

[iskra-vitaly]

Closing this draft to open a normal PR