LLVM_RTLIB_PATH should not hard code linux

The path is incorrect on Darwin. Changed to use $(HOST_OS) instead.

Fixes Darwin build.

Bug: 29275768
Test: Forrest
Change-Id: I164306ad2237bce86baf37d3291622a709bfe8f3
diff --git a/core/clang/config.mk b/core/clang/config.mk
index 63582c2..df9cad2 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -1,6 +1,6 @@
 ## Clang configurations.
 
-LLVM_RTLIB_PATH := $(LLVM_PREBUILTS_PATH)/../lib64/clang/$(LLVM_RELEASE_VERSION)/lib/linux/
+LLVM_RTLIB_PATH := $(LLVM_PREBUILTS_PATH)/../lib64/clang/$(LLVM_RELEASE_VERSION)/lib/$(HOST_OS)/
 
 define convert-to-clang-flags
 $(strip $(filter-out $(CLANG_CONFIG_UNKNOWN_CFLAGS),$(1)))