Problem: "ninja clean" does not fully clean the build directories of
configure-time executables (e.g. syncqt). This can lead to problems when
building with compiler and linker launchers: on configure time, the
launchers are not used (compare CMake issue #20762). After a "ninja
clean", the executable might be removed but the object files are still
there. This leads to a situation where the object files have been
created without the compiler launcher but are linked with the linker
launcher. We encountered a situation however, where the linker launcher
requires the usage of the compiler launcher.
The configure-time executable has a ${target}_build custom command that
runs "cmake --build" and creates a timestamp file to track when to build
the target. To circumvent the problem of stale object files we add the
"--clean-first" argument to that target to fully rebuild configure-time
executables if the timestamp file is out of date.
The performance this imposes is negligible, because
1. Those configure-time executables are seldom out of date.
2. They are supposed to be "tiny executables with system dependencies
only" anyway.
Pick-to: 6.5
Change-Id: I701f9089f5ad941ffdf235aeccc3119b68c4e3e3
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
aad3b1f063