K 10
svn:author
V 8
woodsb02
K 8
svn:date
V 27
2018-03-11T02:24:26.600895Z
K 7
svn:log
V 813
Allow USES=go ports to override make targets & include <bsd.port.pre.mk>

Prior to this change, if a port had:
- USES=go.mk,
- .include <bsd.port.pre.mk>, and
- overrode a make target (e.g. post-extract:)

then the following warnings were produced when invoking make on the port:
  make: "/usr/local/poudriere/ports/default/CATEGORY/PORT/Makefile" line XX: warning: duplicate script for target "post-extract" ignored
  make: "/usr/local/poudriere/ports/default/Mk/Uses/go.mk" line 68: warning: using previous script for "post-extract" defined here

This change fixes this issue by wrapping the definition of make targets
in a separate once-only !defined wrapper which is blocked until post.mk.
This concept was copied from Mk/Uses/python.mk.

PR:		224948
Submitted by:	woodsb02
Approved by:	jlaffaye (maintainer)

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