Make mapcarto-mapnik fails on OS X

[Nicolasribot]

Hi,

Trying to compile magnacarto on Mac OS X Sierra, with mapnik installed from brew, I get:

github.com/omniscale/magnacarto/render/magnacarto-mapnik

/usr/local/Cellar/go/1.7.1/libexec/pkg/tool/darwin_amd64/link: running clang++ failed: exit status 1
Undefined symbols for architecture x86_64:
"_mapnik_version", referenced from:
github.com/omniscale/magnacarto/vendor/github.com/omniscale/go-mapnik._Cvar_mapnik_version in go.o
"_mapnik_version_major", referenced from:
github.com/omniscale/magnacarto/vendor/github.com/omniscale/go-mapnik._Cvar_mapnik_version_major in go.o
"_mapnik_version_minor", referenced from:
github.com/omniscale/magnacarto/vendor/github.com/omniscale/go-mapnik._Cvar_mapnik_version_minor in go.o
"_mapnik_version_patch", referenced from:
github.com/omniscale/magnacarto/vendor/github.com/omniscale/go-mapnik._Cvar_mapnik_version_patch in go.o
"_mapnik_version_string", referenced from:
github.com/omniscale/magnacarto/vendor/github.com/omniscale/go-mapnik._Cvar_mapnik_version_string in go.o
ld: symbol(s) not found for architecture x86_64

Nicolas