I had hoped this question would go away after Emacs 18.57 was released, but people continue to compile 18.55. Easiest solution: upgrade.
This is a result of the SunOS localtime/tzsetwall malloc bug, which was (finally!) fixed in SunOS 4.1.2. If you actually need the full explanation, send me e-mail. If you absolutely must compile Emacs 18.55 (eg., you are compiling Nemacs), the easiest workaround was to put `#define SYSTEM_MALLOC' in src/config.h.
GNU Emacs FAQ: Getting Emacs/Packages