libstream_out_standard_plugin: fix linkage on OS/2

Move freeaddrinfo() to compat/.

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  CCLD     libstream_out_standard_plugin.la
weakld: error: Unresolved symbol (UNDEF) '_freeaddrinfo'.
weakld: info: The symbol is referenced by:
    P:\tmp\ldconv_libstream_out_standard_plugin_48c454704dac1660d0.obj
Ignoring unresolved externals reported from weak prelinker.
Error! E2028: _freeaddrinfo is an undefined reference
file P:/tmp\ldconv_libstream_out_standard_plugin_48c454704dac1660d0.obj(ldconv_libstream_out_standard_plugin_48c454704dac1660d0.obj): undefined symbol _freeaddrinfo
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Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>