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/config.mk b/core/config.mk
index 2d387ef..84ff3fe 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -217,6 +217,13 @@
 combo_2nd_arch_prefix :=
 include $(BUILD_SYSTEM)/combo/select.mk
 
+# Load the 2nd host arch if it's needed.
+ifdef HOST_2ND_ARCH
+combo_target := HOST_
+combo_2nd_arch_prefix := $(HOST_2ND_ARCH_VAR_PREFIX)
+include $(BUILD_SYSTEM)/combo/select.mk
+endif
+
 # on windows, the tools have .exe at the end, and we depend on the
 # host config stuff being done first
 
@@ -357,7 +364,7 @@
 # To run bison from elsewhere you need to set up enviromental variable
 # BISON_PKGDATADIR.
 BISON_PKGDATADIR := $(PWD)/external/bison/data
-BISON := prebuilts/misc/$(BUILD_OS)-$(BUILD_ARCH)/bison/bison
+BISON := prebuilts/misc/$(BUILD_OS)-$(HOST_PREBUILT_ARCH)/bison/bison
 YACC := $(BISON) -d
 
 DOXYGEN:= doxygen
@@ -501,6 +508,17 @@
 $(TARGET_2ND_ARCH_VAR_PREFIX)TARGET_GLOBAL_CPPFLAGS += $($(TARGET_2ND_ARCH_VAR_PREFIX)TARGET_RELEASE_CPPFLAGS)
 endif
 
+ifdef HOST_2ND_ARCH
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_GLOBAL_CFLAGS += $(COMMON_GLOBAL_CFLAGS)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_RELEASE_CFLAGS += $(COMMON_RELEASE_CFLAGS)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_GLOBAL_CPPFLAGS += $(COMMON_GLOBAL_CPPFLAGS)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_RELEASE_CPPFLAGS += $(COMMON_RELEASE_CPPFLAGS)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_GLOBAL_LD_DIRS += -L$($(HOST_2ND_ARCH_VAR_PREFIX)HOST_OUT_INTERMEDIATE_LIBRARIES)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_PROJECT_INCLUDES := $(HOST_PROJECT_INCLUDES)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_GLOBAL_CFLAGS += $($(HOST_2ND_ARCH_VAR_PREFIX)HOST_RELEASE_CFLAGS)
+$(HOST_2ND_ARCH_VAR_PREFIX)HOST_GLOBAL_CPPFLAGS += $($(HOST_2ND_ARCH_VAR_PREFIX)HOST_RELEASE_CPPFLAGS)
+endif
+
 # allow overriding default Java libraries on a per-target basis
 ifeq ($(TARGET_DEFAULT_JAVA_LIBRARIES),)
   TARGET_DEFAULT_JAVA_LIBRARIES := core core-junit ext framework framework2