Allow absolute CMAKE_INSTALL_LIBDIR

CMakeLists.txt

@@ -298,6 +298,11 @@ if(SPDLOG_INSTALL)
     # ---------------------------------------------------------------------------------------
     # Install pkg-config file
     # ---------------------------------------------------------------------------------------
+    if (IS_ABSOLUTE "${CMAKE_INSTALL_LIBDIR}")
+        set(PKG_CONFIG_LIBDIR "${CMAKE_INSTALL_LIBDIR}")
+    else()
+        set(PKG_CONFIG_LIBDIR "\${exec_prefix}/${CMAKE_INSTALL_LIBDIR}")
+    endif()
     get_target_property(PKG_CONFIG_DEFINES spdlog INTERFACE_COMPILE_DEFINITIONS)
     string(REPLACE ";" " -D" PKG_CONFIG_DEFINES "${PKG_CONFIG_DEFINES}")
     string(CONCAT PKG_CONFIG_DEFINES "-D" "${PKG_CONFIG_DEFINES}")

cmake/spdlog.pc.in

@@ -1,7 +1,7 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
 includedir=${prefix}/include
-libdir=${exec_prefix}/@CMAKE_INSTALL_LIBDIR@
+libdir=@PKG_CONFIG_LIBDIR@
 
 Name: lib@PROJECT_NAME@
 Description: Fast C++ logging library.