cmake: Set ENVIRONMENT property for examples on Windows

This change simplifies running examples on Windows, because the DLL
must reside either in the same folder where the executable is or
somewhere in PATH.

examples/CMakeLists.txt

@@ -10,6 +10,13 @@ function(add_example name)
   )
   set(test_name ${name}_example)
   add_test(NAME ${test_name} COMMAND ${target_name})
+  if(BUILD_SHARED_LIBS AND MSVC)
+    # The DLL must reside either in the same folder where the executable is
+    # or somewhere in PATH. Using the latter option.
+    set_tests_properties(${test_name} PROPERTIES
+      ENVIRONMENT "PATH=$<TARGET_FILE_DIR:secp256k1>;$ENV{PATH}"
+    )
+  endif()
 endfunction()
 
 add_example(ecdsa)