Configure instead of trying to build

	Because building invokes the Makefile, which creates another
	`.build_doc` inside of `.build_doc` but it uses the wrong source
	directory without CMakeLists.txt so it fails to actually build.
	But at least it doesn't infinitely configure itself taking up
	all the remaining space in my hard drive :)

doc/sphinx/Makefile

@@ -36,11 +36,10 @@ full-help: $(VENVDIR)
 	@echo "\n\033[1;31mNOTE: This help texts shows unsupported targets!\033[0m"
 	@echo "Run 'make help' to see supported targets."
 
-build_mir:
+configure:
 	. $(VENV); \
 	cd ../../; \
-	cmake -B .build_doc -DMIR_ENABLE_TESTS=NO; \
-	cmake --build .build_doc --target doc;
+	cmake -B .build_doc -DMIR_ENABLE_TESTS=NO -DMIR_PLATFORM=x11;
 
 # Shouldn't assume that venv is available on Ubuntu by default; discussion here:
 # https://bugs.launchpad.net/ubuntu/+source/python3.4/+bug/1290847
@@ -78,7 +77,7 @@ run: install
 	. $(VENV); sphinx-autobuild -b dirhtml "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS)
 
 # Doesn't depend on $(BUILDDIR) to rebuild properly at every run.
-html: install
+html: install configure
 	. $(VENV); cd ../../.build_doc/doc/sphinx; $(SPHINXBUILD) -b dirhtml "$(SOURCEDIR)" "$(BUILDDIR)" -w $(SPHINXDIR)/warnings.txt $(SPHINXOPTS)
 
 epub: install
@@ -97,7 +96,7 @@ clean-doc:
 	git clean -fx "$(BUILDDIR)"
 	rm -rf $(SPHINXDIR)/.doctrees
 
-spelling: build_mir html
+spelling: html
 	. $(VENV) ; cd ../../.build_doc/doc/sphinx/; python3 -m pyspelling -c $(SPHINXDIR)/spellingcheck.yaml -j $(shell nproc)
 
 linkcheck: install