[tlbuild] failure to propagate TL_CONFIGURE_ARGS completely

[Nelson H. F. Beebe]

I think that I may have found a bug in TeX Live 2016 Build script.  It
shows up when I attempt to configure on a system for which even the
latest config.guess does not recognize the platform: MidnightBSD 0.7.

It is a system on which I can normally supply a configure argument like

	--build=x86_64-unknown-freebsd10.2

from a similar system, and that works for several other
non-TeX-related packages, as well as for part of TeX Live.

However, that option supplied in the environment like this:

	 env	TL_MAKE=/usr/local/bin/gmake \
		TL_CONFIGURE_ARGS=--build=x86_64-unknown-freebsd10.2 \
		texlive-20160504/source/Build

fails to propagate to the freetype2 configure script:

	gmake[3]: Entering directory '/local/build/bare/texlive-20160504/source/Work/libs/freetype2'
	rm -rf ft-build
	/usr/local/bin/gmkdir -p ft-build
	cd ft-build && \
	  CC='gcc' CONFIG_SITE=/dev/null CONFIG_SHELL='/bin/sh' \
	  /bin/sh /local/build/bare/texlive-20160504/source/Work/libs/freetype2/../../../libs/freetype2/freetype-src/configure \
	     --disable-shared \
	    --without-bzip2 \
	    --without-zlib \
	    --without-png \
	    --without-harfbuzz \
	    --prefix=/local/build/bare/texlive-20160504/source/Work/libs/freetype2/ft-install \
	    --libdir=/local/build/bare/texlive-20160504/source/Work/libs/freetype2 \
	    --includedir=/local/build/bare/texlive-20160504/source/Work/libs/freetype2
	...
	checking build system type... /local/build/bare/texlive-20160504/source/libs/freetype2/freetype-src/builds/unix/config.guess: unable to guess system type

	This script, last modified 2016-04-02, has failed to recognize
	the operating system you are using.

Presumably this should be relatively easy to fix by someone who
understands the Build script, but I could not quickly spot the error.
Perhaps someone else on this list can.

The bug is show-stopper, and it is possible that there are other
configure scripts in subdirectories later that are also not receiving
a nondefault --build option, so the bug may exist for multiple
subdirectories.

-------------------------------------------------------------------------------
- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- University of Utah                    FAX: +1 801 581 4148                  -
- Department of Mathematics, 110 LCB    Internet e-mail: beebe at math.utah.edu  -
- 155 S 1400 E RM 233                       beebe at acm.org  beebe at computer.org -
- Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe/ -
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