Documentation/sphinx: let the user specify PDFLATEX and LATEXOPTS

Refer to xelatex and latex options via variables. This allows the user
to override the pdflatex and latex options to use on the make command
line for experimenting. As a side effect, this makes the makefile a bit
tidier.
Reviewed-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Documentation/Makefile.sphinx

@@ -10,6 +10,8 @@ _SPHINXDIRS   = $(patsubst $(srctree)/Documentation/%/conf.py,%,$(wildcard $(src
 SPHINX_CONF   = conf.py
 PAPER         =
 BUILDDIR      = $(obj)/output
+PDFLATEX      = xelatex
+LATEXOPTS     = -interaction=nonstopmode
 
 # User-friendly check for sphinx-build
 HAVE_SPHINX := $(shell if which $(SPHINXBUILD) >/dev/null 2>&1; then echo 1; else echo 0; fi)
@@ -29,7 +31,7 @@ else ifneq ($(DOCBOOKS),)
 else # HAVE_SPHINX
 
 # User-friendly check for pdflatex
-HAVE_PDFLATEX := $(shell if which xelatex >/dev/null 2>&1; then echo 1; else echo 0; fi)
+HAVE_PDFLATEX := $(shell if which $(PDFLATEX) >/dev/null 2>&1; then echo 1; else echo 0; fi)
 
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
@@ -68,7 +70,7 @@ htmldocs:
 
 latexdocs:
 ifeq ($(HAVE_PDFLATEX),0)
-	$(warning The 'xelatex' command was not found. Make sure you have it installed and in PATH to produce PDF output.)
+	$(warning The '$(PDFLATEX)' command was not found. Make sure you have it installed and in PATH to produce PDF output.)
 	@echo "  SKIP    Sphinx $@ target."
 else # HAVE_PDFLATEX
 	@$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,latex,$(var),latex,$(var)))
@@ -76,7 +78,8 @@ endif # HAVE_PDFLATEX
 
 pdfdocs: latexdocs
 ifneq ($(HAVE_PDFLATEX),0)
-	$(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=xelatex LATEXOPTS="-interaction=nonstopmode" -C $(BUILDDIR)/$(var)/latex)
+	$(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=$(PDFLATEX) LATEXOPTS="$(LATEXOPTS)" -C $(BUILDDIR)/$(var)/latex)
+
 endif # HAVE_PDFLATEX
 
 epubdocs: