Let the OS clear new large strings of NUL
On my platform, this sped up (make-string 4000000000 0) from 2.5 to 0.015 seconds (not that people should want to do this much :-). * src/alloc.c (allocate_string_data): New arg CLEARIT. Callers changed. (Fmake_string): Prefer calloc to malloc+memset when allocating a large string of NUL bytes. (make_clear_string): New function. (make_uninit_string): Use it. (make_clear_multibyte_string): New function. (make_uninit_multibyte_string): Use it.