acinclude.m4:
  Use AC_LANG_PUSH/POP instead of _SAVE/RESTORE
  Add test to get type of 'struct rlimit'
  Switch order of including stdlib.h and declaration being tested to
  match how it will be used in regular code.
configure.in:
  Call MYSQL_TYPE_STRUCT_RLIMIT macro
sql/mysqld.cc:
  Use STRUCT_RLIMIT for getting type of struct rlimit.