[CMake] Don't wrap command in ROOTTEST_COMPILE_MACRO in CMake target

[guitargeek]

Wrapping to command inside a Cmake target doesn't seem to be necessary,
because in the test, the target is forced to be built without
dependencies anyway
(e.g. cmake --build . --target my_macro_test/fast --always-make when
using makefiles).

This fixes spurious project rebuilds when running the macro tests when
using ninja without forcing to run the test in serial mode.

[github-actions]

Test Results

    20 files      20 suites   3d 15h 7m 57s ⏱️
 3 653 tests  3 649 ✅   0 💤 4 ❌
71 384 runs  71 166 ✅ 213 💤 5 ❌

For more details on these failures, see this check.

Results for commit c4ce0be.

♻️ This comment has been updated with latest results.

[hahnjo]

Wrapping to command inside a Cmake target doesn't seem to be necessary, because in the test, the target is forced to be built without dependencies anyway (e.g. cmake --build . --target my_macro_test/fast --always-make when using makefiles).

This is only partially true, for Unix Makefiles. With Ninja, we don't use /fast nor --always-make AFAICT

[guitargeek]

The intention of the original macro is apparently to only build this one target that runs the command. The fact that this was not done correctly for Ninja doesn't mean that rebuilding all dependencies was the intended behavior. I suppose it was just not correctly implemented.

[guitargeek]

Note that this warning is never hit. Nowhere in the codebase to we specify DEPENDS in a ROOTTEST_COMPILE_MACRO. Together with the dependencies being ignored via the \fast target when using Makefiles, that makes it clear to me that it was never the intention to have dependencies for these macro tests.

The problem is that even with no dependencies, a re-configuration will still be triggered if the CMake code was changed, which is the reason thy the RUN_SERIAL true workaround was needed.