[libc++abi] Actually set POSITION_INDEPENDENT_CODE when building shared library

This is a bug fix from https://reviews.llvm.org/D60005.

Differential Revision: https://reviews.llvm.org/D60158

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@357550 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 7123718..f8b31c1 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -176,7 +176,9 @@
   cxxabi_object_library(cxxabi_static_objects)
 endif()
 
-cxxabi_object_library(cxxabi_shared_objects POSITION_INDEPENDENT_CODE ON)
+cxxabi_object_library(cxxabi_shared_objects)
+set_target_properties(cxxabi_shared_objects PROPERTIES POSITION_INDEPENDENT_CODE ON)
+
 set(cxxabi_static_sources $<TARGET_OBJECTS:cxxabi_static_objects>)
 set(cxxabi_shared_sources $<TARGET_OBJECTS:cxxabi_shared_objects>)