core: Explicitly add GPG_ERROR_CFLAGS
core: Explicitly add GPG_ERROR_CFLAGS

* src/Makefile.am (AM_CFLAGS): Add GPG_ERROR_CFLAGS

--
This fixes the include directory for libgpg error if
it is installed in a different prefix then libassuan. Previously
libassuan provided the include directory also implicitly.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme