[Codegen] Decrease minimum jump table density.

[Codegen] Decrease minimum jump table density.

Minimum density for both optsize and non optsize are now options
-sparse-jump-table-density (default 10) for non optsize functions
-dense-jump-table-density (default 40) for optsize functions, which
matches the current default. This improves several benchmarks at google
at the cost of a small codesize increase. For code compiled with -Os,
the old behavior continues

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264689 91177308-0d34-0410-b5e6-96231b3b80d8