CLHEP LCG_97 Update, master branch (2020.04.03.)

See merge request atlas/atlasexternals!652

See SPI-1576 for some more details.

GeoModelTools Tweaks, master branch (2020.03.30.)

See merge request atlas/atlasexternals!649

It would've kind of worked in the previous setup still, but it seemed
best to make these fixes nevertheless.

GeoModelTools tag update

See merge request atlas/atlasexternals!648

Update GeoModelIO version

Closes ATLASSIM-4477 and ATLASDD-35

See merge request atlas/atlasexternals!646

CheckerGccPlugins: New/missed warnings

See merge request atlas/atlasexternals!645

We normally warn about a potential threaded problem if there's a call
to AttributeList::~AttributeList.  Suppress the warning if the argument
is a variable that was declared thread-safe.

Fix error in documentation.

The real algorithm base class is now `Gaudi::Algorithm'; `Algorithm' is
a compatibility layer deriving from it.

Upadate the Gaudi inheritance checker to also warn about deriving from
Gaudi::Algorithm instead of AthAlgorithm.

The thread-safety checker verifies that when virtual functions are overridden,
they have compatible threading attributes.  However, in some cases
involving multiple inheritance, this check was being skipped.
Fixed.

It's unsafe in general to copy coral::AttributeList objects, due to
bugs in CORAL.  Try to warn about instances of this.

Disable GeoModelTools, master branch (2020.03.16.)

See merge request !640

This is necessary as this version of GeoModelTools produces a
library (XMLParser) that has a name clash with a library coming
from ROOT.

flake8_atlas: Improve OutputLevel checks

See merge request !639

Bump acts v0.17.0, enable the JSON plugin

See merge request !613

atlas_add_test: Fix return code if post.sh is not available

See merge request !638

The OutputLevel checker (ATL900) will now also flag the following:
```
  MyAlg(OutputLevel=DEBUG)
```

CheckerGccPlugins: Allow declaring constructors / destructors as not-thread-safe.

See merge request !637

This fixes a bug introduced with !607. In case the `post.sh` script is
not available, the unit test wrapper was returning 0 exit code even if
the test failed. This would only affect projects that do not build
`AtlasTest/TestTools`.

Allow attaching a not_thread_safe attribute to constructors and destructors.

This is actually a bit annoying, because gcc versions prior to 10 will not
accept a c++11-style attribute after a ctor/dtor declaration.  It will
accept the __attribute__ form, except that in that case, one can't
use a scoped attribute.  So need to introduce an alias for
ATLAS::not_thread_safe, called ATLAS_not_thread_safe.
As a result of this, we also need to introduce a separate macro
to use in this context: ATLAS_CTORDTOR_NOT_THREAD_SAFE.

At this point, we also change the gnu:: prefix on the attributes
in checker_macros.h to ATLAS::.  (Prior to gcc version 7, one could
not use a prefix other than gnu::.)

GeoModel Updates, master branch (2020.03.11.)

See merge request !636

Used the opportunity to also tweak the CMake configuration of the
package just a little bit.

So that VP1LightExternals could build it in cases when it's
not available from the system, or from an LCG release.

Finally removing the source code from the repository...

Merge remote-tracking branch 'rbianchi/master-geomodel-updates' into GeoModelUpdates-master-20200311

VP1LightExternals Fixes, master branch (2020.03.11.)

See merge request !635

By adding the Davix and TBB packages to it, to make sure that
ROOT can be built successfully in a standalone way, if it
would be necessary.

So that it would work on the x86_64-ubuntu1804-gcc8-opt
platform as well...

In a setup where LCG is not available for a given platform, LCG_FOUND
was kept as FALSE in a cache variable. Preventing the "renewed"
find_package(...) call from being successful.

Since the caller may very well not have used the REQUIRED
keyword of find_package(...). A warning is still warranted
though, to tell the caller why LCG was not found. (And
because find_package(...) will anyway print a warning itself
after everything...)

CheckerGccPlugins: Allow marking initialize()/finalize() not thread-safe.

See merge request !633

macOS Catalina Fixes, master branch (2020.03.11.)

See merge request !634

Similar to the other cases, I had to set up the configuration of the
code through a helper script, to pass all flags to the autoconfiguration
script.

As it turns out the linker itself needs the double dollar signs.
The problem here was that since we now configure the Python build
through a BASH shell script, we need to make sure that the dollar
signs are properly escaped. (ExternalProject_Add(...) was doing
this behind the scenes in the past.)