macOS: use precompiled libraries for arm64 build

Standard wiki build instructions for building Blender on macOS can now be used
on Macs with ARM processors.

This contains all libraries except for Embree and OpenImageDenoise, so Cycles
performance does not yet have full performance and features in this build. An
x86-64 build is likely to still render faster than arm64 until Embree is added.

Uses the new lib/darwin_arm64 folder. For simplicity and to keep download size
under control, both for end users and builders, we are not planning to ship
universal binaries. So this is a separate folder from lib/darwin.

Ref T78710

Differential Revision: https://developer.blender.org/D10276

GNUmakefile

@@ -183,8 +183,13 @@ endif
 ifndef DEPS_INSTALL_DIR
 	DEPS_INSTALL_DIR:=$(shell dirname "$(BLENDER_DIR)")/lib/$(OS_NCASE)
 
-	ifneq ($(OS_NCASE),darwin)
-		# Add processor type to directory name
+	# Add processor type to directory name, except for darwin x86_64
+	# which by convention does not have it.
+	ifeq ($(OS_NCASE),darwin)
+		ifneq ($(CPU),x86_64)
+			DEPS_INSTALL_DIR:=$(DEPS_INSTALL_DIR)_$(CPU)
+		endif
+	else
 		DEPS_INSTALL_DIR:=$(DEPS_INSTALL_DIR)_$(CPU)
 	endif
 endif
@@ -198,7 +203,7 @@ endif
 # in libraries, or python 2 for running make update to get it.
 ifeq ($(OS_NCASE),darwin)
 	ifeq (, $(shell command -v $(PYTHON)))
-		PYTHON:=../lib/darwin/python/bin/python3.7m
+		PYTHON:=$(DEPS_INSTALL_DIR)/python/bin/python3.7m
 		ifeq (, $(shell command -v $(PYTHON)))
 			PYTHON:=python
 		endif