Execute build scripts directly from source (issue 545870043 by address@hidden)

[lemzwerg]

LGTM, with some nits.


https://codereview.appspot.com/545870043/diff/549860043/make/doc-i18n-root-rules.make
File make/doc-i18n-root-rules.make (right):

https://codereview.appspot.com/545870043/diff/549860043/make/doc-i18n-root-rules.make#newcode10
make/doc-i18n-root-rules.make:10: find $(outdir)/$* -name '*.html' |
xargs grep -L 'UNTRANSLATED NODE: IGNORE ME' | sed 's!$(outdir)/!!g' |
xargs $(PYTHON) $(buildscript-dir)/mass-link.py --prepend-suffix
.$(ISOLANG) hard $(outdir) $(top-build-dir)/Documentation/$(outdir)
If you are going to change that please shorten the lines to 80 chars if
possible.

https://codereview.appspot.com/545870043/diff/549860043/scripts/build/help2man.pl
File scripts/build/help2man.pl (left):

https://codereview.appspot.com/545870043/diff/549860043/scripts/build/help2man.pl#oldcode1
scripts/build/help2man.pl:1: #!@PERL@ -w
Not sure whether this is useful – help2man.pl is not part of LilyPond
but gets imported, so I think it's best if it stays unchanged.  Please
check!

https://codereview.appspot.com/545870043/diff/549860043/scripts/build/mf2pt1.pl
File scripts/build/mf2pt1.pl (left):

https://codereview.appspot.com/545870043/diff/549860043/scripts/build/mf2pt1.pl#oldcode1
scripts/build/mf2pt1.pl:1: #!@PERL@
Again an imported script, which should ideally stay unmodified for easy
import of newer versions.

https://codereview.appspot.com/545870043/