Fix use of not thread safe function localtime()

[ricrogz]

localtime() is not thread safe (https://linux.die.net/man/3/localtime):

The four functions asctime(), ctime(), gmtime() and localtime() return a pointer to static data and hence are not thread-safe.
Thread-safe versions asctime_r(), ctime_r(), gmtime_r() and localtime_r() are specified by SUSv2, and available since libc 5.2.5.

RDkit uses localtime() in logging, and the thread sanitizer flags its usage as a data race. Fortunately, it's easy to fix.

[greglandrum]

We should probably switch this code to use C++ time functions, but that’s clearly a different PR