Add basic Darwin+Arm64 support as HOST_CROSS

Soong will use this to turn on universal binary support (X86_64 + Arm64
in the same binary).

Bug: 203607969
Test: m sdk-repo-platform-tools sdk-repo-build-tools on Mac
Change-Id: I04612136a42e85f4add95202ce20e741d9aaa302
diff --git a/core/combo/select.mk b/core/combo/select.mk
index 33c8e6d..7617558 100644
--- a/core/combo/select.mk
+++ b/core/combo/select.mk
@@ -27,6 +27,13 @@
 combo_var_prefix := $(combo_2nd_arch_prefix)$(combo_target)
 
 # Set reasonable defaults for the various variables
+ifeq ($(combo_target),HOST_CROSS_)
+$(KATI_obsolete_var \
+  $(combo_var_prefix)GLOBAL_ARFLAGS \
+  $(combo_var_prefix)STATIC_LIB_SUFFIX \
+  $(combo_var_prefix)transform-shared-lib-to-toc \
+  ,HOST_CROSS builds are not supported in Make)
+else
 
 $(combo_var_prefix)GLOBAL_ARFLAGS := crsPD -format=gnu
 
@@ -34,3 +41,5 @@
 
 # Now include the combo for this specific target.
 include $(BUILD_COMBOS)/$(combo_target)$(combo_os_arch).mk
+
+endif