fixed hardcoded paths with variables. (capstone-engine#1018)

* fixed hardcoded paths with variables.

cmake pkg-config file fixed hardcoded paths with variables. CMakeLists.txt line 394 needs to be modified
> configure_file("capstone.pc.in" "capstone.pc" @only)

* forgot to add 64bit support variable.

capstone.pc.in

@@ -1,7 +1,12 @@
+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=${prefix}
+libdir=${prefix}/lib@LIBSUFFIX@
+includedir=${prefix}/include
+
 Name: capstone
 Description: Capstone disassembly engine
 Version: @VERSION_MAJOR@.@VERSION_MINOR@.@VERSION_PATCH@
 URL: http://www.capstone-engine.org
-archive=@CMAKE_INSTALL_PREFIX@/lib/libcapstone.a
-Libs: -L@CMAKE_INSTALL_PREFIX@/lib -lcapstone
-Cflags: -I@CMAKE_INSTALL_PREFIX@/include/capstone
+archive=${libdir}/libcapstone.a
+Libs: -L${libdir} -lcapstone
+Cflags: -I${includedir}