Index: llvm/cmake/config-ix.cmake
===================================================================
--- llvm/cmake/config-ix.cmake
+++ llvm/cmake/config-ix.cmake
@@ -474,7 +474,8 @@
   set(strdup "_strdup")
 
   # See if the DIA SDK is available and usable.
-  set(MSVC_DIA_SDK_DIR "$ENV{VSINSTALLDIR}DIA SDK")
+  set(MSVC_DIA_SDK_DIR "$ENV{VSINSTALLDIR}DIA SDK" CACHE STRING
+      "Path to the DIA SDK")
 
   # Due to a bug in MSVC 2013's installation software, it is possible
   # for MSVC 2013 to write the DIA SDK into the Visual Studio 2012