`cmake --install` did not propagate per-script failures into its
process exit code.
In parallel mode, cmInstallScriptHandler::Install spawned each install
script as a child process but never inspected the child exit status or
termination signal, and always returned 0. It now reads each child's
status after the event loop, prints the failing script's exit code or
signal, and returns non-zero if any script failed. A failed parallel
install also no longer writes the combined install_manifest.txt, so a
partial manifest is not mistaken for a complete install.
In serial mode, GetScripts() returns the top-level cmake_install.cmake
once per component and per configuration, so multiple scripts run only
when installing several components or configurations at once. The loop
overwrote its result on every iteration, so an earlier script that
failed via cmake_language(EXIT) was masked by a later one that
succeeded. The loop now stops at the first failure. This is a no-op
for a single component and configuration; it changes only installs of
multiple components or configurations, which now stop at the first
failed script and report it instead of attempting the rest.
Fixes: #27906
The install tests check that the output matches content including the
"status" portion of the output. Unset the variable to avoid leakage from
development environments.
Daksh Mamodiya
Robert Maynard
AJIOB
Ben Boeckel
Martin Duffy