[ng] diag: new make function $(am.fatal)

Mostly a preparatory patch for future changes.

* lib/am/header-vars.mk (am.fatal): New.
* automake.in (generate_makefile): Use in instead of $(error) in the
generated make code exiting for earlier errors.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
2 files changed