Add generation of registry file for pkg-config

.pkg-config/taocpp-json.pc.in

@@ -0,0 +1,7 @@
+includedir="@CMAKE_INSTALL_FULL_INCLUDEDIR@"
+
+Name: @PROJECT_NAME@
+Description: taoJSON is a C++ header-only JSON library
+Version: @PROJECT_VERSION@
+URL: https://github.com/taocpp/json
+Cflags: -I${includedir}

CMakeLists.txt

@@ -12,6 +12,7 @@ include(GNUInstallDirs)
 
 set(TAOCPP_JSON_INSTALL_DOC_DIR "${CMAKE_INSTALL_DOCDIR}/tao/json" CACHE STRING "The installation doc directory")
 set(TAOCPP_JSON_INSTALL_CMAKE_DIR "${CMAKE_INSTALL_DATAROOTDIR}/${PROJECT_NAME}/cmake" CACHE STRING "The installation cmake directory")
+set(TAOCPP_JSON_INSTALL_PKGCONFIG_DIR "${CMAKE_INSTALL_DATAROOTDIR}/pkgconfig" CACHE STRING "The installation pkgconfig directory")
 
 # define a header-only library
 add_library(taocpp-json INTERFACE)
@@ -61,13 +62,20 @@ option(TAOCPP_JSON_INSTALL "Generate the install target" ${TAOCPP_JSON_IS_MAIN_P
 if(TAOCPP_JSON_INSTALL)
  include(CMakePackageConfigHelpers)
 
- # Make package findable
+ # Make package findable by CMake
  configure_package_config_file(.cmake/taocpp-json-config.cmake.in ${PROJECT_NAME}-config.cmake
  INSTALL_DESTINATION ${TAOCPP_JSON_INSTALL_CMAKE_DIR}
  NO_CHECK_REQUIRED_COMPONENTS_MACRO
  NO_SET_AND_CHECK_MACRO
  )
 
+ # Make package findable by pkg-config
+ configure_package_config_file(.pkg-config/taocpp-json.pc.in ${PROJECT_NAME}.pc
+ INSTALL_DESTINATION ${TAOCPP_JSON_INSTALL_PKGCONFIG_DIR}
+ NO_CHECK_REQUIRED_COMPONENTS_MACRO
+ NO_SET_AND_CHECK_MACRO
+ )
+
  # Ignore pointer width differences since this is a header-only library
  unset(CMAKE_SIZEOF_VOID_P)
 
@@ -84,6 +92,10 @@ if(TAOCPP_JSON_INSTALL)
  ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}-config-version.cmake
  DESTINATION ${TAOCPP_JSON_INSTALL_CMAKE_DIR}
  )
+ install(FILES
+ ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc
+ DESTINATION ${TAOCPP_JSON_INSTALL_PKGCONFIG_DIR}
+ )
  install(EXPORT ${PROJECT_NAME}-targets
  NAMESPACE taocpp::
  DESTINATION ${TAOCPP_JSON_INSTALL_CMAKE_DIR}