The test sometimes crashes with ASLR enabled. This seems to happen when
regcomp() grows the process stack and happens to run into the virtual
memory limit set at the beginning of the test. ASLR triggers the
problem since it introduces a bit of fragmentation and thus introduces
cases where stack allocation can be the trigger of virtual memory
exhaustion, instead of dynamic memory allocation in regcomp().
Make the test stable by priming the stack before doing anything else.
This effectively reserves 16MB of virtual memory for the stack, which in
practice is enough to make the test stable on amd64.
PR: 259971