[RFC patch] Documenation: don't build media .rst files when not building Documentation/media/

[Randy Dunlap]

Don't build media .rst files from header files when Documentation/media/
is not in the target SPHINXDIRS.

It looks like the dependencies in Documentation/media/Makefile should
take care of running parse-headers.pl to generated .rst files from the
header files, but it's not happening and I don't see why not.

---
 Documentation/Makefile |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- linux-next-20180426.orig/Documentation/Makefile
+++ linux-next-20180426/Documentation/Makefile
@@ -52,8 +52,7 @@ loop_cmd = $(echo-cmd) $(cmd_$(1)) || ex
 #    e.g. "media" for the linux-tv book-set at ./Documentation/media
 
 quiet_cmd_sphinx = SPHINX  $@ --> file://$(abspath $(BUILDDIR)/$3/$4)
-      cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media $2 && \
-	PYTHONDONTWRITEBYTECODE=1 \
+      cmd_sphinx = PYTHONDONTWRITEBYTECODE=1 \
 	BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(srctree)/$(src)/$5/$(SPHINX_CONF)) \
 	$(SPHINXBUILD) \
 	-b $2 \