http_compression.cpp fails to build when using zlib with a Z_PREFIX

[bryan-lipinski]

zconf.h contains defines that rename zlib functions when buliding with -DZ_PREFIX. This leaves the following #define active in http_compression.cpp:

#    define compress              z_compress

This renames the 'compress' functions of zlib_compressor_base causing the build to fail with:

error: allocating an object of abstract class type 'web::http::compression::builtin::gzip_compressor'
    return std::unique_ptr<_Type>(new _Type());