[build] Fix Makefile based build.

This fixes the Python include path after the GYP files have been
relocated into another directory.

R=machenbach@chromium.org

Review-Url: https://codereview.chromium.org/1938893002
Cr-Commit-Position: refs/heads/master@{#35928}

Makefile

@@ -448,7 +448,7 @@ $(OUT_MAKEFILES): $(GYPFILES) $(ENVFILE)
 	$(eval CXX_TARGET_ARCH:=$(subst aarch64,arm64,$(CXX_TARGET_ARCH)))
 	$(eval CXX_TARGET_ARCH:=$(subst x86_64,x64,$(CXX_TARGET_ARCH)))
 	$(eval V8_TARGET_ARCH:=$(subst .,,$(suffix $(basename $@))))
-	PYTHONPATH="$(shell pwd)/tools/generate_shim_headers:$(shell pwd)/build:$(PYTHONPATH):$(shell pwd)/tools/gyp/pylib:$(PYTHONPATH)" \
+	PYTHONPATH="$(shell pwd)/tools/generate_shim_headers:$(shell pwd)/gypfiles:$(PYTHONPATH):$(shell pwd)/tools/gyp/pylib:$(PYTHONPATH)" \
 	GYP_GENERATORS=make \
 	tools/gyp/gyp --generator-output="$(OUTDIR)" gypfiles/all.gyp \
 	              -Igypfiles/standalone.gypi --depth=. \