Add SPDX license identifier to fail1.adb also.

Oops, missed one file from the first go.
Add SPDX license identifiers to source code.

To help the automatic scanners to identify the license
of the source code, add SPDX license identifiers as
specified at

In our case, the line is:

 SPDX-License-Identifier: ISC

for every file.
Fix Library_Type comparison in uses '' quotation marks to wrap the -DLibrary_Type="static"
option. This causes the Lubrary_Type symbol to have "" marks in it.
Add build status links to README.
Oops, add missing semicolon to

Attempt #2 for fix.
Fix typo in

s/#endif/#end if/. This makes the ahven.gpr installation to work.
Remove gnat_linux dynamic build from Debian setup as well.

gprbind raises assert_failure during the build, so makes no sense
to use the gnat_linux build system on Debian 10.
Remove static builds from Debian setup.

Currently the static builds don't work as expected on Debian 10.
Add Fedora setup to builds.
Move .builds.yml to .builds/debian.yml.

This makes space for multiple different build configurations.
Fix build manifest and reorder builds.
Add build steps for gnat_linux static and dynamic variants.
Link ahven tests with -lgnarl when using static lib.
Fix tester execution and use gprbuild by default.

As gnatmake is these days just a wrapper for gprbuild,
use gprbuild as a default. Older systems with "real" gnatmake
can still override the GNAT_BUILDER.
Fix static library build.

When Ahven is build as a static library, we need to add
linker option '-lgnarl' during the linking. Otherwise,
we get a lot of errors about missing functions when compiling
the actual test runner.

Also, define Library_Interface at the top level, so
the static build also has it. This fixes the include
dir population.
Added tag ahven-2.8 for changeset 275a2332c0bb
Update for 2.8.

Update the Debian package installation section (patch
from Nicolas Boulenguez) and remove the obsolete
documentation links.
Update NEWS.txt for 2.8
Link the shared library with LDFLAGS.

Comfignat transmits them to gprbuild via -largs, which affects
executables but not libraries.

From Nicolas Boulenguez, thanks!