Set default LOCAL_MULTILIB only if LOCAL_MODULE_HOST_ARCH isn't restricted

Otherwise we may end up conflict between LOCAL_MODULE_HOST_ARCH and the
default multilib mode.
Also removed the unneeded variants of LOCAL_MODULE_HOST_ARCH.

Change-Id: I9e5a0144da3cb6310be0ddf098738987e51305de
diff --git a/core/host_shared_library.mk b/core/host_shared_library.mk
index 2fdf61f..438a9ce 100644
--- a/core/host_shared_library.mk
+++ b/core/host_shared_library.mk
@@ -1,6 +1,7 @@
 my_prefix := HOST_
 include $(BUILD_SYSTEM)/multilib.mk
 
+ifndef LOCAL_MODULE_HOST_ARCH
 ifndef my_module_multilib
 ifeq ($(HOST_PREFER_32_BIT),true)
 my_module_multilib := 32
@@ -9,6 +10,7 @@
 my_module_multilib := first
 endif
 endif
+endif
 
 LOCAL_2ND_ARCH_VAR_PREFIX :=
 include $(BUILD_SYSTEM)/module_arch_supported.mk