R600: Do not predicated basic block with multiple alu clause

R600: Do not predicated basic block with multiple alu clause

Test is not included as it is several 1000 lines long.
To test this functionnality, a test case must generate at least 2 ALU clauses,
where an ALU clause is ~110 instructions long.

NOTE: This is a candidate for the stable branch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185943 91177308-0d34-0410-b5e6-96231b3b80d8