pkg/52390: current fails to bootstrap on CentOS 6

[bacon4000%gmail.com@localhost]

>Number:         52390
>Category:       pkg
>Synopsis:       current fails to bootstrap on CentOS 6
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 10 19:05:00 +0000 2017
>Originator:     Jason Bacon
>Release:        pkgsrc-current 2017-07-10
>Organization:
UW Milwaukee
>Environment:
Linux centosdev.local 2.6.32-696.3.2.el6.x86_64 #1 SMP Tue Jun 20 01:26:55 UTC 2017 x86_64 x86_64 x86_64 GNU/Linu
>Description:
Bootstrap is failing as follows:

cc -O2 -D_GNU_SOURCE=1 -D_FORTIFY_SOURCE=2  -Wall -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wno-uninitialized -Wreturn-type -Wcast-qual -Wpointer-arith -Wwrite-strings -Wswitch -Wshadow -Werror  -DHAVE_NBCOMPAT_H=1 -I/home/bacon/Pkgsrc/pkg-2017-07-10/work/wrk/pkgtools/cwrappers/work/libnbcompat -DNEED_MI_VECTOR_HASH -c fixup-libtool.c
cc1: warnings being treated as errors
fixup-libtool.c: In function 'process_option':
fixup-libtool.c:247: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
fixup-libtool.c: In function 'process_variable':
fixup-libtool.c:275: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
fixup-libtool.c: In function 'fixup_libtool_la':
fixup-libtool.c:348: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
fixup-libtool.c:354: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
fixup-libtool.c:372: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
fixup-libtool.c:382: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
*** [fixup-libtool.o] Error code 1

bmake: stopped in /home/bacon/Pkgsrc/pkg-2017-07-10/work/wrk/pkgtools/cwrappers/work/cwrappers-20170611
1 error

bmake: stopped in /home/bacon/Pkgsrc/pkg-2017-07-10/work/wrk/pkgtools/cwrappers/work/cwrappers-20170611
*** Error code 2

Stop.
bmake[1]: stopped in /home/bacon/Pkgsrc/pkgsrc-2017-07-10/pkgtools/cwrappers
*** Error code 1

Stop.
bmake: stopped in /home/bacon/Pkgsrc/pkgsrc-2017-07-10/pkgtools/cwrappers
===> exited with status 1
aborted.

This is a recent regression, as I have bootstrapped current on the same machine up to about a week ago.
>How-To-Repeat:
Bootstrap current on a pristine CentOS 6 installation.
>Fix: