AC_FUNC_MMAP changes to AC_CHECK_FUNCS(mmap)


configure.in:
  don't use AC_FUNC_MMAP - it checks for "private fixed mapping of
  already-mapped memory" - and we don't care about it.
  use regular AC_CHECK_FUNCS(mmap) instead
  (blame autoconf for misleading macro name - should've been
  AC_MMAP_CAN_DO_PRIVATE_FIXING_MAPPING_OF_ALREADY_MAPPED_MEMORY :)
include/my_pthread.h:
  not all cpp's understand #warning :-[]