Thomas Haller authored Jan 29, 2021 and Philip Withnall committed Feb 01, 2021

We preallocate buffers that are used after forked. That is because
malloc()/free() are not async-signal-safe and must not be used between
fork() and exec().

However, for the child process that exits without fork, valgrind wrongly
reports these buffers as leaked.
That can be suppressed with "--child-silent-after-fork=yes", but it is
cumbersome.

Work around by trying to allocate the buffers on the stack. At
least in the common cases where the pointers are small enough
so that we can reasonably do that.

If the buffers happen to be large, we still allocate them on the heap
and the problem still happens. Maybe we could have also allocated them
as thread_local, but currently glib doesn't use that.

[smcv: Cosmetic adjustments to address review comments from pwithnall]