diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -149,6 +149,7 @@
     cmake_push_check_state()
     list(APPEND CMAKE_REQUIRED_INCLUDES ${LIBXML2_INCLUDE_DIRS})
     list(APPEND CMAKE_REQUIRED_LIBRARIES ${LIBXML2_LIBRARIES})
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS ${LIBXML2_DEFINITIONS})
     check_symbol_exists(xmlReadMemory libxml/xmlreader.h HAVE_LIBXML2)
     cmake_pop_check_state()
     if(LLVM_ENABLE_LIBXML2 STREQUAL FORCE_ON AND NOT HAVE_LIBXML2)