build,cares,openssl,zlib: limit symbol exports

[bnoordhuis]

Refs: #4932 #6274

On Windows, Node exports a curated list of symbols from its dependencies that don't use dllimport/dllexport (c-ares, openssl, zlib)

On Unices, Node indiscriminately re-exports everything thanks to -Wl,--whole-archive.

There's a comment about it in node.gyp:

# TODO(bnoordhuis) Make all platforms export the same list of symbols.
# Teach mkssldef.py to generate linker maps that UNIX linkers understand.

It would be good to implement that. It should help trim down the binary size.

[sam-github]

/cc @nicolasnoble

[bnoordhuis]

nodejs/node-gyp#1755 points out that symbols from deps/histogram are also exported (and conflict with symbols from an add-on.)

[jasnell]

@bnoordhuis ... what's left here to do?