Implemented instruction counter for LLVM IR.

Enabled by passing flag print_llvm_ir_instruction_count to impalad.

Sample output:

===-------------------------------------------------------------------------===
                         ... Instruction Counts ...
===-------------------------------------------------------------------------===
2  Binary                             Number of Binary instructions.
4  Other                              Number of Other instructions.
5  Terminator                         Number of Terminator instructions.
===-------------------------------------------------------------------------===
                              ... Totals ...
===-------------------------------------------------------------------------===
5  Total Blocks                       Number of Blocks in module.
1  Total Functions                    Number of Functions in module.
11 Total Instruction                  Number of Total Instructions.

Change-Id: I565d2bf8e084c71448ee312e38b6dc7a96cc20b6
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3603
Reviewed-by: Paden Tomasello <paden.tomasello@cloudera.com>
Tested-by: jenkins
(cherry picked from commit 931fc83502d9a553c4f481e0db87c30a0c26467c)
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4088
Reviewed-by: Henry Robinson <henry@cloudera.com>