In #359 I identify a race condition between multiple parallel invocations
of cmake, which can arise naturally during ctests. Now that the file
contents will not change without an intervening git commit, it is
sufficient to ensure that the parallel invocations use distinct temporary
file names with high probability.
As analyzed in #359, if the header contains the current time, it will
be updated while running the testsuite; this, in turn, causes multiple
cmake processes to attempt to update targets like lib/libexpress.so.2.0.0
at the same time, causing test failures.
