Remove unused LLVM related codes of directory:be/src/exec (#2910)
there are many LLVM related codes in code base, but these codes are not really used.
The higher version of GCC is not compatible with the LLVM 3.4.2 version currently used by Doris.
The PR delete all LLVM related code of directory: be/src/exec.
Now size of HyperLogLog struct is so large that it lead the rowset is
too small when ingesting data. In this CL, registers in HyperLogLog are
only created when it is needed. When ingesting data, it's normal case
that there are only few values in one HyperLogLog.
The new msg of limit exceed: "Memory exceed limit. %msg, Backend:%ip, fragment:%id Used:% , Limit:%. xxx".
This commit unifies the msg of 'Memory exceed limit' such as check_query_state, RETURN_IF_LIMIT_EXCEEDED and LIMIT_EXCEEDED.
