Use CMAKE_INSTALL_FULL_LIBDIR, CMAKE_INSTALL_FULL_INCLUDEDIR

Do not roll our own path contatenation, let's use
GNUInstallDirs macros to do the work.

CMakeLists.txt

@@ -28,19 +28,6 @@ SET (VERSION ${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_REVISION})
 
 LIST (APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake/")
 include(GNUInstallDirs)
-SET (prefix ${CMAKE_INSTALL_PREFIX})
-SET (exec_prefix ${CMAKE_INSTALL_PREFIX})
-IF (IS_ABSOLUTE ${CMAKE_INSTALL_LIBDIR})
-    SET (libdir ${CMAKE_INSTALL_LIBDIR})
-ELSE ()
-    SET (libdir "\${prefix}/${CMAKE_INSTALL_LIBDIR}")
-ENDIF ()
-IF (IS_ABSOLUTE ${CMAKE_INSTALL_INCLUDEDIR})
-    SET (includedir ${CMAKE_INSTALL_INCLUDEDIR})
-ELSE ()
-    SET (includedir "\${prefix}/${CMAKE_INSTALL_INCLUDEDIR}")
-ENDIF ()
-
 OPTION (MSGPACK_32BIT "32bit compile" OFF)
 
 INCLUDE(TestBigEndian)
@@ -245,14 +232,6 @@ IF ("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "sparc")
     SET (CMAKE_C_FLAGS   "-DMSGPACK_ZONE_ALIGN=8 ${CMAKE_C_FLAGS}")
 ENDIF ()
 
-IF (NOT DEFINED CMAKE_INSTALL_BINDIR)
-    SET(CMAKE_INSTALL_BINDIR bin)
-ENDIF ()
-
-IF (NOT DEFINED CMAKE_INSTALL_LIBDIR)
-    SET(CMAKE_INSTALL_LIBDIR lib)
-ENDIF ()
-
 IF (MSGPACK_BUILD_EXAMPLES)
     ADD_SUBDIRECTORY (example)
 ENDIF ()

msgpack-c.pc.in

@@ -1,10 +1,5 @@
-prefix=@prefix@
-exec_prefix=@exec_prefix@
-libdir=@libdir@
-includedir=@includedir@
-
 Name: MessagePack
 Description: Binary-based efficient object serialization library
 Version: @VERSION@
-Libs: -L${libdir} -lmsgpack-c
-Cflags: -I${includedir}
+Libs: -L@CMAKE_INSTALL_FULL_LIBDIR@ -lmsgpack-c
+Cflags: -I@CMAKE-INSTALL_FULL_INCLUDEDIR@