build: support compiling .mm on host

libchrome uses .mm (Objective-C++) files to bridge C++ code with
OS X Frameworks. This adds support for compiling .mm to .o by just
using the existing C++ support.

Bug: 24168923
Change-Id: Ia65357e2e2584dfffcb6796e214fe6b27635c3a6

core/binary.mk

@@ -926,6 +926,20 @@ $(objc_objects): $(intermediates)/%.o: $(TOPDIR)$(LOCAL_PATH)/%.m $(yacc_cpps) $
 -include $(objc_objects:%.o=%.P)
 endif
 
+###########################################################
+## ObjC++: Compile .mm files to .o
+###########################################################
+
+objcpp_sources := $(filter %.mm,$(my_src_files))
+objcpp_objects := $(addprefix $(intermediates)/,$(objcpp_sources:.mm=.o))
+
+ifneq ($(strip $(objcpp_objects)),)
+$(objcpp_objects): $(intermediates)/%.o: $(TOPDIR)$(LOCAL_PATH)/%.mm $(yacc_cpps) $(proto_generated_headers) \
+    $(my_additional_dependencies)
+	$(transform-$(PRIVATE_HOST)mm-to-o)
+-include $(objcpp_objects:%.o=%.P)
+endif
+
 ###########################################################
 ## AS: Compile .S files to .o.
 ###########################################################
@@ -1039,6 +1053,7 @@ normal_objects := \
     $(c_objects) \
     $(gen_c_objects) \
     $(objc_objects) \
+    $(objcpp_objects) \
     $(yacc_objects) \
     $(lex_objects) \
     $(proto_generated_objects) \