* support building libgpc as Mach shared library

   * `GPC_Initialize' and `GPC_Finalize' available as user routines (to
     help building shared libraries)

   * better warnings for unexpected results of string comparisons

   * handle `volatile' attribute on types

   * allow `asm' in any dialect (if the `asm' keyword is enabled)

   * support for gcc-4.1.x