cmake: Report skipped tests properly

[hebasto]

CMake allows to report about skipped tests properly instead of passing dummy test cases. For instance, on Windows:

> ctest --build-config Release -R compilerbug
Test project C:/Users/hebasto/source/repos/bitcoin/build
    Start 26: compilerbug_tests
1/1 Test #26: compilerbug_tests ................***Skipped   0.02 sec

100% tests passed, 0 tests failed out of 1

Total Test time (real) =   0.04 sec

The following tests did not run:
         26 - compilerbug_tests (Skipped)

We have 3 such cases:

• src/test/compilerbug_tests.cpp
• src/test/raii_event_tests.cpp
• src/test/system_tests.cpp

This PR handles the first two cases.

Once bitcoin#30454 is merged, the following lines can be deleted:

bitcoin/src/test/system_tests.cpp

Lines 19 to 25 in 9b4aa92

	// At least one test is required (in case ENABLE_EXTERNAL_SIGNER is not defined).
	// Workaround for https://github.com/bitcoin/bitcoin/issues/19128
	BOOST_AUTO_TEST_CASE(dummy)
	{
	BOOST_CHECK(true);
	}

[hebasto]

cc @maflcko @theuni

[hebasto]

From https://github.com/hebasto/bitcoin/actions/runs/10015755552/job/27687669760:

...
        Start  27: compilerbug_tests
 24/133 Test  #27: compilerbug_tests ....................***Skipped   0.02 sec
...

100% tests passed, 0 tests failed out of 133

Total Test time (real) = 252.67 sec

The following tests did not run:
	 27 - compilerbug_tests (Skipped)

[maflcko]

lgtm

[maflcko]

Any reason to even support this? Seems fine to just let devs call $build_dir/test_bitcoin -t suite/case manually for now (just like in autotools)?

[hebasto]

This allows leveraging parallelism when running ctest -j <number_of_jobs>. Basically, this mirrors the behaviour of make check in the master branch.