Adding support for a custom target dir while building, fixing a few issues where the SITE.ipc folder/file was not created for a fresh build

Removing the copy and lib from the path, so you can build the x1tst example without using the run script

Fixing undefined refrence on debian 11, adding better error messages, replacing uses in two file of RCG_DIR with the newer env var RCG_SRC, adding gitignore in test/ directory so you can run the 'run' script without generating files tracked by git

Modify test/x1tst.mdl to include every part that still works (MATRIX is broken).
Add tests to build, install and run models.
/opt/rtcds needs to work and be writeable by the testing user for install and run to work.
tests are part of cmake and run with ctest on the command line.

rcgtest: tests made more 'rcg directory' agnostic.  Some race conditions that could fail tests improved.

rcg: Moved sequence check into /src/python dir.  Improved sequence error message.  Fixed some typos and formatting issues.

test is implemented as a python script in test/python_modules/sequence/

test compares the calculation sequence to the calculation graph.

The test is run during compilation after parsing but before building.  By default, a failure will kill compilation, but
if IGNORE_SEQUENCE_ERRORS=1 in the environment, only a warning will be issued and compilation will continue.

Two out-of-order bugs are fixed.

1. Ordering simply counts how many inputs of a part of visited. When that number matches the total inputs for the part, the part is visited,
but inside a subystem, delays were counted twice.  Once on the initial pass looking for signal sources, and again as a normal part.

Parts that took input directly from delays could appear early in the sequence.

This change skips following links form delays as a normal part.

2. If a data source, including subsystem inputs, constants, delays, grounds were connected directly to a subsystem output, then
parts immediately connected from the output would be added to the subsystem sequence, though they were at a higher level.

This bug could cause these parts to be sequenced out of order.

Change is to check whether a part leading form a data source is in the subsystem.  This check is already included when following from normal (non-input) parts.

rcgtest.pl refactored and "all" test group added.

RCG test: reverted oscillator test files back to those in master branch.  They contain tighter references for when an oscillator part is newly started.  Probably the references in this branch were taken on old oscillators.