Support host multilib build

This change basically ported our target multilib to the host side.
It supports 2 host build modes: x86 and x86_64 multilib build.
For now you need to set "BUILD_HOST_64bit=true" to switch to x86_64
multilib build. Later we'll default to x86_64 build and have a flag
to force 32-bit only build, which may be needed by SDK build.

In host module definition, like in target ones, you can use the
following
LOCAL variables to set up multilib configuration:
LOCAL_MULTILIB: can be "both", "first", "32" or "64".
It also supports the same set of arch or 32-vs-64 specific LOCAL
variables.
By default, it builds only for the first arch.

To keep path compatibility, in x86_64 build files are still output to
out/host/linux-x86; Both 32-bit and 64-bit executables are in
out/host/linux-86/bin;
In x86_64 build 32-bit shared libraries are installed to
out/host/linux-x86/lib32
and 64-bit shared libraries are installed to out/host/linux-x86/lib;
32-bit object files are output to out/host/linux-x86/obj32 and 64-bit
object files
are output to out/host/linux-x86/obj.

Bug: 13751317
Change-Id: I6044f83b7db369a33e05209e8c588eb6dc83409f
diff --git a/core/host_shared_library_internal.mk b/core/host_shared_library_internal.mk
new file mode 100644
index 0000000..d9769d3
--- /dev/null
+++ b/core/host_shared_library_internal.mk
@@ -0,0 +1,46 @@
+###########################################################
+## Standard rules for building a normal shared library.
+##
+## Additional inputs from base_rules.make:
+## None.
+##
+## LOCAL_MODULE_SUFFIX will be set for you.
+###########################################################
+
+LOCAL_IS_HOST_MODULE := true
+
+ifeq ($(strip $(LOCAL_MODULE_CLASS)),)
+LOCAL_MODULE_CLASS := SHARED_LIBRARIES
+endif
+ifeq ($(strip $(LOCAL_MODULE_SUFFIX)),)
+LOCAL_MODULE_SUFFIX := $(HOST_SHLIB_SUFFIX)
+endif
+ifneq ($(strip $(OVERRIDE_BUILT_MODULE_PATH)),)
+$(error $(LOCAL_PATH): Illegal use of OVERRIDE_BUILT_MODULE_PATH)
+endif
+ifneq ($(strip $(LOCAL_MODULE_STEM)$(LOCAL_BUILT_MODULE_STEM)),)
+$(error $(LOCAL_PATH): Cannot set module stem for a library)
+endif
+
+$(call host-shared-library-hook)
+
+skip_build_from_source :=
+ifdef LOCAL_PREBUILT_MODULE_FILE
+ifeq (,$(call if-build-from-source,$(LOCAL_MODULE),$(LOCAL_PATH)))
+include $(BUILD_SYSTEM)/prebuilt_internal.mk
+skip_build_from_source := true
+endif
+endif
+
+ifndef skip_build_from_source
+
+# Put the built modules of all shared libraries in a common directory
+# to simplify the link line.
+OVERRIDE_BUILT_MODULE_PATH := $($(LOCAL_2ND_ARCH_VAR_PREFIX)HOST_OUT_INTERMEDIATE_LIBRARIES)
+
+include $(BUILD_SYSTEM)/binary.mk
+
+$(LOCAL_BUILT_MODULE): $(all_objects) $(all_libraries) $(LOCAL_ADDITIONAL_DEPENDENCIES)
+	$(transform-host-o-to-shared-lib)
+
+endif  # skip_build_from_source