Fixed PCRE2 beng built when CMake is configured

The bundled PCRE2 library will be built as a separate target and configuring
CMake no longer builds it. Instead, it will only be built when it is out of date.
This requires all targets to declare that they depend on the pcre2 target in
order for it to be built.

cmake/BuildPCRE2.cmake

@@ -1,16 +1,22 @@
 # Build the PCRE2 library from source
+#
+# This will add a 'pcre2' target to CMake which will generate the libpcre2-8.so
+# dynamic library and the pcre2.h header. If your target requires PCRE2 you
+# need to add a dependeny on the 'pcre2' target by adding add_dependencies(<target> pcre2)
+# to the CMakeLists.txt
+
 set(PCRE_ROOT_DIR ${CMAKE_SOURCE_DIR}/pcre2/)
 set(PCRE_BUILD_DIR ${CMAKE_BINARY_DIR}/pcre2/)
-
+set(PCRE2_LIBRARIES ${CMAKE_BINARY_DIR}/pcre2/libpcre2-8.so CACHE STRING "PCRE2 dynamic libraries" FORCE)
 execute_process(COMMAND ${CMAKE_COMMAND} -E make_directory ${PCRE_BUILD_DIR})
 execute_process(COMMAND ${CMAKE_COMMAND} -E copy_directory ${PCRE_ROOT_DIR} ${PCRE_BUILD_DIR})
-execute_process(COMMAND ${CMAKE_COMMAND} ${PCRE_BUILD_DIR}
+
+add_custom_target(pcre2 COMMAND ${CMAKE_COMMAND} ${PCRE_BUILD_DIR}
   -DBUILD_SHARED_LIBS=Y
   -DPCRE2_BUILD_PCRE2GREP=N
   -DPCRE2_BUILD_TESTS=N
+  COMMAND make
   WORKING_DIRECTORY ${PCRE_BUILD_DIR})
-execute_process(COMMAND make WORKING_DIRECTORY ${PCRE_BUILD_DIR})
 
-set(PCRE2_LIBRARIES ${CMAKE_BINARY_DIR}/pcre2/libpcre2-8.so CACHE STRING "PCRE2 dynamic libraries" FORCE)
 include_directories(${CMAKE_BINARY_DIR}/pcre2/)
 install(PROGRAMS ${PCRE2_LIBRARIES} DESTINATION ${MAXSCALE_LIBDIR})