make latexpdf after make latex rebuilds latex sources

[jfbu]

Procedure to reproduce the problem

With any project, make latexpdf will unneedlessly rebuild the latex source files even immediately afer make latex.

This is noticeable on big enough projects such as Sphinx own docs.

Expected results

make latexpdf should behave like make -C <builddir> all-pdf when there is no need to rebuild the latex files.

Environment info

• OS: Mac
• Python version: 3.6.4
• Sphinx version: 1.6.5

May be relevant to #4343

edit

This actually applies to make latex itself: if executed twice in a row with no intervening changes, it still re-creates the tex file (which takes time on big projects).

[jfbu]

For example when building Sphinx documentation at my locale, I currently get typically:

The LaTeX files are in _build/latex.
Run 'make' in that directory to run these through (pdf)latex
(use `make latexpdf' here to do that automatically).

real	0m45.885s
user	0m45.703s
sys	0m0.172s

And if I now do

$ time make -C _build/latex all-pdf

this gives

real	0m9.943s
user	0m9.660s
sys	0m0.258s

This is why it is frustrating that make latexpdf immediately following make latex redoes all the Sphinx phase which amounts for most of the build time.

[tk0miya]

Fixed by #5085.
Please let me know if it does not work well.