Support Mac-arm64 target, fixes #218 (#222)

Makefile

@@ -71,6 +71,9 @@ mac-x86:
 mac-x86_64:
 	docker run -it --rm -v $$PWD:/workdir -e CROSS_TRIPLE=x86_64-apple-darwin multiarch/crossbuild make clean-native native OS_NAME=Mac OS_ARCH=x86_64
 
+mac-arm64:
+	docker run -it --rm -v $$PWD:/src -e TARGET=arm64-apple-darwin mcandre/snek:darwin sh -c "make clean-native native CROSS_PREFIX=arm64-apple-darwin20.4- OS_NAME=Mac OS_ARCH=arm64"
+
 freebsd-x86:
 	docker run -it --rm -v $$PWD:/workdir empterdose/freebsd-cross-build:9.3 make clean-native native CROSS_PREFIX=i386-freebsd9- OS_NAME=FreeBSD OS_ARCH=x86
 

Makefile.common

@@ -1,6 +1,6 @@
 # os=Default is meant to be generic unix/linux
 
-known_targets := Linux-x86 Linux-x86_64 Linux-arm Linux-armv6 Linux-armv7 Linux-android-arm Linux-ppc64 Mac-x86 Mac-x86_64 DragonFly-x86_64 FreeBSD-x86_64 OpenBSD-x86_64 Windows-x86 Windows-x86_64 SunOS-sparcv9 HPUX-ia64_32
+known_targets := Linux-x86 Linux-x86_64 Linux-arm Linux-armv6 Linux-armv7 Linux-android-arm Linux-ppc64 Mac-x86 Mac-x86_64 Mac-arm64 DragonFly-x86_64 FreeBSD-x86_64 OpenBSD-x86_64 Windows-x86 Windows-x86_64 SunOS-sparcv9 HPUX-ia64_32
 target := $(OS_NAME)-$(OS_ARCH)
 
 ifeq (,$(findstring $(strip $(target)),$(known_targets)))
@@ -126,6 +126,14 @@ Mac-x86_64_LINKFLAGS := -dynamiclib
 Mac-x86_64_LIBNAME   := libjansi.jnilib
 Mac-x86_64_JANSI_FLAGS  := 
 
+Mac-arm64_CC        := $(CROSS_PREFIX)clang -v
+Mac-arm64_STRIP     := $(CROSS_PREFIX)strip -x
+MAC_SDK := /usr/local/osxcross/SDK/MacOSX11.3.sdk/
+Mac-arm64_CCFLAGS    := -I$(MAC_SDK)/System/Library/Frameworks/JavaVM.framework/Headers  -Isrc/main/lib/inc_mac -Os -fPIC -mmacosx-version-min=11.0 -fvisibility=hidden
+Mac-arm64_LINKFLAGS := -shared
+Mac-arm64_LIBNAME   := libjansi.jnilib
+Mac-arm64_JANSI_FLAGS  :=
+
 Windows-x86_CC           := $(CROSS_PREFIX)gcc
 Windows-x86_STRIP        := $(CROSS_PREFIX)strip
 Windows-x86_CCFLAGS      := -D_JNI_IMPLEMENTATION_ -Isrc/main/lib/inc_win -Os