gprbuild not configured to find gnat compiler

lsb_release -rd
Description: Ubuntu 19.04
Release: 19.04

% apt-cache policy gprbuild
gprbuild:
  Installed: 2018-6
  Candidate: 2018-6
  Version table:
 *** 2018-6 500
        500 http://be.archive.ubuntu.com/ubuntu disco/universe amd64 Packages
        100 /var/lib/dpkg/status

trying to compile a hello world Ada project I get the following error message:

% gprbuild -P hello.gpr
No valid configuration found
Generation of configuration files failed
GNAT-TEMP-000001.TMP:1:01: "project" expected
gprbuild: processing of configuration project "/tmp/GNAT-TEMP-000001.TMP" failed

gprconfig is not aware of any compilers:
% gprconfig
No compilers found for target x86_64-pc-linux-gnu

although I have gnat installed:

% apt-cache policy gnat
gnat:
  Installed: 8.0.1ubuntu1
  Candidate: 8.0.1ubuntu1
  Version table:
 *** 8.0.1ubuntu1 500
        500 http://be.archive.ubuntu.com/ubuntu disco/universe amd64 Packages
        100 /var/lib/dpkg/status

if I work around this by using a config.cgpr form an older ubuntu systems I am able to compile.

according to my ada expert this indicates a problem with the gprbuild package.

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: gprbuild 2018-6
ProcVersionSignature: Ubuntu 5.0.0-15.16-generic 5.0.6
Uname: Linux 5.0.0-15-generic x86_64
ApportVersion: 2.20.10-0ubuntu27
Architecture: amd64
CurrentDesktop: GNOME
Date: Tue May 28 10:44:44 2019
InstallationDate: Installed on 2019-04-19 (39 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
SourcePackage: gprbuild
UpgradeStatus: No upgrade log present (probably fresh install)