Index: llvm/cmake/modules/FindZ3.cmake
===================================================================
--- llvm/cmake/modules/FindZ3.cmake
+++ llvm/cmake/modules/FindZ3.cmake
@@ -3,7 +3,7 @@
 # Function to check Z3's version
 function(check_z3_version z3_include z3_lib)
   # The program that will be executed to print Z3's version.
-  file(WRITE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testz3.c
+  file(WRITE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testz3.cpp
        "#include <assert.h>
         #include <z3.h>
         int main() {
@@ -16,13 +16,19 @@
   # Get lib path
   get_filename_component(z3_lib_path ${z3_lib} PATH)
 
+  # Try to find a threading module in case Z3 was built with threading support.
+  # Threads are required elsewhere in LLVM, but not marked as required here because
+  # Z3 could have been compiled without threading support.
+  find_package(Threads)
+  set(z3_link_libs "-lz3" "${CMAKE_THREAD_LIBS_INIT}")
+
   try_run(
     Z3_RETURNCODE
     Z3_COMPILED
     ${CMAKE_BINARY_DIR}
-    ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testz3.c
+    ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testz3.cpp
     COMPILE_DEFINITIONS -I"${z3_include}"
-    LINK_LIBRARIES -L${z3_lib_path} -lz3
+    LINK_LIBRARIES -L${z3_lib_path} ${z3_link_libs}
     RUN_OUTPUT_VARIABLE SRC_OUTPUT
   )