n-api: mark symbols as hidden
When building N-API externally, symbols need to be marked as hidden, otherwise, between versions 8.0.0 and 8.6.0 the symbols from Node.js will be used, which have a different signature thus causing segfaults.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
n-api