Make macOS arm64 default to target macOS 11 in Makefile

Makefile

@@ -445,6 +445,12 @@ ifeq ($(PLATFORM),darwin)
   # Default minimum Mac OS X version
   ifeq ($(MACOSX_VERSION_MIN),)
     MACOSX_VERSION_MIN=10.7
+    ifneq ($(findstring $(ARCH),ppc ppc64),)
+      MACOSX_VERSION_MIN=10.5
+    endif
+    ifeq ($(ARCH),arm64)
+      MACOSX_VERSION_MIN=11.0
+    endif
   endif
 
   MACOSX_MAJOR=$(shell echo $(MACOSX_VERSION_MIN) | cut -d. -f1)