Build: add scripts to build dependencies for Windows and macOS.

Note these are intended for platform maintainers, we do not intend to
support users making their own builds with these. For that precompiled
libraries from lib/ should be used.

Implemented by Martijn Berger, Ray Molenkamp and Brecht Van Lommel.

Differential Revision: https://developer.blender.org/D2753

GNUmakefile

@@ -43,6 +43,11 @@ ifndef BUILD_DIR
 	BUILD_DIR:=$(shell dirname "$(BLENDER_DIR)")/build_$(OS_NCASE)
 endif
 
+# Dependencies DIR's
+DEPS_SOURCE_DIR:=$(BLENDER_DIR)/build_files/build_environment
+DEPS_BUILD_DIR:=$(BUILD_DIR)/deps
+DEPS_INSTALL_DIR:=$(shell dirname "$(BLENDER_DIR)")/lib/$(OS_NCASE)
+
 # Allow to use alternative binary (pypy3, etc)
 ifndef PYTHON
 	PYTHON:=python3
@@ -146,6 +151,27 @@ cycles: all
 headless: all
 bpy: all
 
+# -----------------------------------------------------------------------------
+# Build dependencies
+DEPS_TARGET = install
+ifneq "$(findstring clean, $(MAKECMDGOALS))" ""
+	DEPS_TARGET = clean
+endif
+
+deps: .FORCE
+	@echo
+	@echo Configuring dependencies in \"$(DEPS_BUILD_DIR)\"
+
+	@cmake -H"$(DEPS_SOURCE_DIR)" \
+	       -B"$(DEPS_BUILD_DIR)" \
+		   -DHARVEST_TARGET=$(DEPS_INSTALL_DIR)
+
+	@echo
+	@echo Building dependencies ...
+	$(MAKE) -C "$(DEPS_BUILD_DIR)" -s -j $(NPROCS) $(DEPS_TARGET)
+	@echo
+	@echo Dependencies successfully built and installed to $(DEPS_INSTALL_DIR).
+	@echo
 
 # -----------------------------------------------------------------------------
 # Configuration (save some cd'ing around)
@@ -164,6 +190,7 @@ help: .FORCE
 	@echo "  * headless  - build without an interface (renderfarm or server automation)"
 	@echo "  * cycles    - build Cycles standalone only, without Blender"
 	@echo "  * bpy       - build as a python module which can be loaded from python directly"
+	@echo "  * deps      - build library dependencies (intended only for platform maintainers)"
 	@echo ""
 	@echo "  * config    - run cmake configuration tool to set build options"
 	@echo ""