/usr/include/AvailabilityInternal.h:22938:10: error: unterminated conditional directive

The syntax of /usr/include/AvailabilityInternal.h is illegal, at least in the eyes of your C compiler.
For every "#if" there needs to be a corresponding "#endif", and the C pre-processor hasn't found those requisite occurrences of "#endif". (All other errors are probably a consequence of this.)

I suppose one could fix the offending file, but if you're using the system perl (as I suspect you are) then I believe that, instead of using cpan, it's recommended that you install modules using your system's package manager.
/usr/include/AvailabilityInternal.h wouldn't even be looked at if you were to install WWW::Curl::Easy using the package manager.

Update: See
https://stackoverflow.com/questions/42031921/unterminated-unconditional-directive-error-when-preprocessing-c-code
if you wish to persevere with a cpanp installation.

Cheers,
Rob

In reply to Re: installing WWW::Curl::Easy perl module in OS X 10.12.6 by syphilis
in thread installing WWW::Curl::Easy perl module in OS X 10.12.6 by igods

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