pkg/53104: warning: Couldn't read shell's output for ... xproto.pc

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         53104
>Category:       pkg
>Synopsis:       warning: Couldn't read shell's output for ... xproto.pc
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 16 18:45:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD 7.1.1
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

Several packages are failing to build for me on NetBSD 7.1.1.
To make sure it's not just a problem with my existing installation,
I installed a fresh copy of 7.1.1 and a fresh copy of the current
pkgsrc from CVS, and tried to build one of the failing packages,
graphics/py-matplotlib-gtk2, using all default settings
(no /etc/mk.conf).

I immediately got a large number of warning messages:

# cd /usr/pkgsrc/graphics/py-matplotlib-gtk2/
# make install
make[4]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[3]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[3]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[2]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[3]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[2]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[2]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[1]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"
make[3]: "../../mk/buildlink3/../../mk/buildlink3/pkgconfig-builtin.mk" line 55: warning: Couldn't read shell's output for "/usr/bin/sed -n  -e 's/Version: 7\.0\.31/2018.1/p'  -e 's/Version: 7\.0\.32/2018.4/p'  /usr/X11R7/lib/pkgconfig/xproto.pc"

Before I start filing separate PRs about all the packages that fail to
build, I figured I should report the very first problem I encountered,
in case the other issues are somehow cascading from this one.

>How-To-Repeat:

See above.

>Fix: