cmake: Add a new spdlog.pc pkgconfig file.

Fixes https://github.com/gabime/spdlog/issues/1237.

CMakeLists.txt

@@ -86,6 +86,7 @@ set(SPDLOG_SRCS
         src/file_sinks.cpp
         src/async.cpp)
 
+set(SPDLOG_CFLAGS "${PROJECT_NAME}")
 
 if (SPDLOG_BUILD_SHARED)
     if(WIN32)
@@ -128,6 +129,8 @@ if(SPDLOG_FMT_EXTERNAL)
         find_package(fmt REQUIRED)
     endif ()
 
+    set(SPDLOG_CFLAGS "${SPDLOG_CFLAGS} -DSPDLOG_FMT_EXTERNAL")
+
     target_compile_definitions(spdlog PUBLIC SPDLOG_FMT_EXTERNAL)
     target_link_libraries(spdlog PUBLIC fmt::fmt)
 
@@ -180,6 +183,8 @@ if (SPDLOG_INSTALL)
     set(config_targets_file "spdlogConfigTargets.cmake")
     set(version_config_file "${CMAKE_CURRENT_BINARY_DIR}/spdlogConfigVersion.cmake")
     set(export_dest_dir "${CMAKE_INSTALL_LIBDIR}/spdlog/cmake")
+    set(pkgconfig_install_dir "${CMAKE_INSTALL_LIBDIR}/pkgconfig")
+    set(pkg_config "${CMAKE_BINARY_DIR}/${PROJECT_NAME}.pc")
 
     #---------------------------------------------------------------------------------------
     # Include files
@@ -190,6 +195,9 @@ if (SPDLOG_INSTALL)
     #---------------------------------------------------------------------------------------
     # Package and version files
     #---------------------------------------------------------------------------------------
+    configure_file("cmake/${PROJECT_NAME}.pc.in" "${pkg_config}" @ONLY)
+    install(FILES "${pkg_config}" DESTINATION "${pkgconfig_install_dir}")
+
     install(EXPORT spdlog
             DESTINATION ${export_dest_dir}
             NAMESPACE spdlog::

cmake/spdlog.pc.in

+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=${prefix}
+includedir=${prefix}/include
+libdir=${exec_prefix}/@CMAKE_INSTALL_LIBDIR@
+
+Name: lib@PROJECT_NAME@
+Description: Fast C++ logging library.
+URL: https://github.com/gabime/@PROJECT_NAME@
+Version: @SPDLOG_VERSION@
+CFlags: -I${includedir}/@SPDLOG_CFLAGS@
+Libs: -L${libdir}/@PROJECT_NAME@ -l@PROJECT_NAME@