[test-suite/doc] Add list of programs we might add.

Add a list of benchmarks, applications and algorithms which are under
discussion to be added to the test-suite.

The initial list includes the the benchmarks mentioned at
https://llvm.org/PR34216, missing SPEC benchmarks, some image processing
algorithms and a few others. The bug tracker only allows adding to the
discussion, not removing, commenting, adding details to individual
benchmarks.

The first proposal was to add these benchmark into the test-suite
repository, but after a discussion, adding it to llvm/docs/Proposals
seem more appropriate. One advantage is that llvm.org will have a
browsable web page with these suggestions.

Suggested-by: Hal Finkel

Differential Revision: https://reviews.llvm.org/D46714

llvm-svn: 345074