gpg-error-config: Determine output at configure time.
* src/gpg-error-config.in (isubdirafter): Remove. Also for --cflags and --libs. * configure.ac (GPG_ERROR_CONFIG_ISUBDIRAFTER): Remove. (GPG_ERROR_CONFIG_CFLAGS): Add -idirafter gpg-extra for W32CE. (GPG_ERROR_CONFIG_CFLAGS): Decide here if adding -I$includedir. (GPG_ERROR_CONFIG_LIBS): Decide here if adding -L$libdir.
Don't do string substitution at the time of its command invocation,
but let it determine at configure time.