Update ICU testing and usage.

test/cmake_subdir_test_icu/CMakeLists.txt

@@ -0,0 +1,22 @@
+# Copyright 2018, 2019 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.5...3.16)
+
+project(cmake_subdir_test LANGUAGES CXX)
+
+add_subdirectory(../.. boostorg/regex)
+add_subdirectory(../../../config boostorg/config)
+add_subdirectory(../../../core boostorg/core)
+add_subdirectory(../../../assert boostorg/assert)
+add_subdirectory(../../../throw_exception boostorg/throw_exception)
+add_subdirectory(../../../predef boostorg/predef)
+
+add_executable(quick_icu ../quick_icu.cpp)
+target_link_libraries(quick_icu Boost::regex_icu)
+
+enable_testing()
+add_test(quick_icu quick_icu)
+
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)