Fix for SAPPHIRE-12162/SAPPHIRE-12122: fix unstable PR_LocalTimeParameters by
#define-ing HAVE_POINTER_LOCALTIME_R and HAVE_LOCALTIME_R. These #define's
cause the compiler to use the threadsafe localtime_r function instead of
localtime when determining PR_LocalTimeParameters, which avoids changes in
PR_LocalTimeParameters at inopportune times (such as computing
GetNextWeeklyOccurrence).

In addition, PR_LocalTimeParameters will always call tzset() when populating
offsets to guarantee that the most current timezone information will be used.