[Ada] Add Sphinx option -W to treat warnings as errors

2018-01-11  Ben Brosgol  <brosgol@adacore.com>

gcc/ada/

	* doc/Makefile: Add Sphinx option -W to treat warnings as errors.

From-SVN: r256506

gcc/ada/ChangeLog

 2018-01-11  Ben Brosgol  <brosgol@adacore.com>
 
+	* doc/Makefile: Add Sphinx option -W to treat warnings as errors.
+
+2018-01-11  Ben Brosgol  <brosgol@adacore.com>
+
 	* doc/gnat_rm/implementation_defined_aspects.rst: Minor type/wording
 	corrections.
 	* gnat_rm.texi: Regenerate.

gcc/ada/doc/Makefile

 # Makefile for Sphinx documentation
 
 # You can set these variables from the command line.
-SPHINXOPTS    =
+SPHINXOPTS    = -W
 SPHINXBUILD   = DOC_NAME=$* sphinx-build
 PAPER         =
 BUILDDIR      = build