Sync with src/config.in.

Sync with src/config.in.
(DO_BLOCK_INPUT, HAVE_DIFFTIME, HAVE_LOCALE_H, HAVE_MEMCMP)
(HAVE_MEMCPY, HAVE_MEMMOVE, HAVE_MEMSET, HAVE_SETITIMER)
(HAVE_SIZE_T, HAVE_SYS_IOCTL_H, HAVE_SYS_PARAM_H, HAVE_SYS_STAT_H)
(HAVE_SYS_TYPES_H, TIME_WITH_SYS_TIME, SYNC_INPUT): Define them.
[__MRC__] (HAVE_ALLOCA_H): Likewise.
(config_machfile, config_opsysfile, my_strftime): New macros.
(HAVE_PWD_H): Move from s-mac.h.
(HAVE_ALLOCA, C_ALLOCA): Move from m-mac.h.
(PTR): Move to s-mac.h.