Allow undefined symbols if we are loading libbcc dynamically.

Bug: http://b/31320715
Bug: http://b/32305815

Test: Run RenderScript tests (host tests for slang and libbcc, RsTest,
CTS)

Change-Id: I0c5d9f8b6c7d9c59893f5adb1da748b280c99f82
diff --git a/Android.mk b/Android.mk
index 4ed3ebd..d7628e5 100644
--- a/Android.mk
+++ b/Android.mk
@@ -103,6 +103,7 @@
 
 ifeq ($(CAN_BUILD_HOST_LLVM_LOADABLE_MODULE),true)
 LOCAL_STATIC_LIBRARIES_linux += libLLVMLinker
+LOCAL_ALLOW_UNDEFINED_SYMBOLS_linux := true
 else
 LOCAL_SHARED_LIBRARIES_linux += libLLVM
 endif