* Refactored split compare pass to be more efficient in LTO usage and allow splitting to other minimum bitwidths.
Efficiency: avoid looping over the whole llvm module N times, when once is also enough.
Bitwidth: Previously, due to fallthrough in switch-case, all comparisons were split to 8-bit, which might not be desirable e.g., 16 or 32 bit might be enough. So now all comparison are split until they are smaller or equal to the target bitwidth, which is controlled through the `AFL_LLVM_LAF_SPLIT_COMPARES_BITW` environment variable.
* fixed miscompilation due to incorrectly trying to split a signed comparison operator
* minor formatting updates and use IRBuilder when inserting multiple instructions
* added @hexcoder-'s test-int_cases.c to make test
* Avoid recursion; switch to smallvector in splitAndSimplify; use switch case for icmp type;
* Fixed issue when splitting < where the inverse comparison was not further split
* some cleanup
* Variable AFL_EXIT_ON_TIME description has been added.
Variables AFL_EXIT_ON_TIME and afl_exit_on_time has been added.
afl->exit_on_time variable initialization has been added.
The asignment of a value to the afl->afl_env.afl_exit_on_time variable from
environment variables has been added.
Code to exit on timeout if new path not found has been added.
* Type of afl_exit_on_time variable has been changed.
Variable exit_on_time has been added to the afl_state_t structure.
* Command `export AFL_EXIT_WHEN_DONE=1` has been added.
* Millisecond to second conversion has been added.
Call get_cur_time() has been added.
* Revert to using the saved current time value.
* Useless check has been removed.
