Add lib directory to linker paths when using libunwind

When using libunwind and not building as standalone project, we
need to add LLVM library directory to the list of linker directories
to ensure it can find libunwind dependency.

Differential Revision: https://reviews.llvm.org/D23287

llvm-svn: 278076

libcxxabi/src/CMakeLists.txt

@@ -55,6 +55,9 @@ endif()
 append_if(libraries LIBCXXABI_HAS_C_LIB c)
 
 if (LIBCXXABI_USE_LLVM_UNWINDER)
+  if (NOT LIBCXXABI_BUILT_STANDALONE)
+    link_directories(${LLVM_LIBRARY_DIR})
+  endif()
   list(APPEND libraries unwind)
 else()
   append_if(libraries LIBCXXABI_HAS_GCC_S_LIB gcc_s)