devel/git: unbreak build with devel/utf8cpp installed

[jbeich]

Summary

Unbreak build with devel/utf8cpp installed

Let preprocessor know ${LOCALBASE}/include is a system include path,
so #include "..." shouldn't try to pick headers from there. lang/gcc*
and lang/clang* already do the right thing.

PR: 196220
Approved by: garga (maintainer)
Approved by: bapt (mentor)

Test Plan

poudriere testport logs:
http://slexy.org/view/s20joohs3Y (8.4R amd64)
http://slexy.org/view/s21fKiZbjw (9.3R i386)
http://slexy.org/view/s2qD15wUqT (10.0R amd64)
http://slexy.org/view/s21c8e3WqI (10.1R i386)

[bapt]

This looks good to me and after this commit we should probably generalize this to the whole ports tree (with caution)

Wait for @garga approval as well.

[garga]

It looks good to me too.

[jbeich]

Closed by commit rP377892 (authored by @jbeich).