Add test reproducing ASAN-like hangs

Backtraces suggest that AddressSanitizer replaces malloc() with a
function that

- locks a mutex and
- calls clock_gettime() while the mutex is held

This commit adds a test that implements a trivial malloc() that behaves
similarly. Currently, this test hangs.

Signed-off-by: Uli Schlachter <psychon@znc.in>