Add Effcee as an optional dependency for use in tests. In future it will
be a required dependency.
Effcee is a stateful pattern matcher that has much of the functionality
of LLVM's FileCheck, except in library form. Effcee makes it much easier
to write tests for optimization passes.
Demonstrate its use in a test for the strength-reduction pass.
Update README.md with example commands of how to get sources.
Update Appveyor and Travis-CI build rules.
Also: Include test libraries if not SPIRV_SKIP_TESTS
- SPIRV_SKIP_TESTS is implied by SPIRV_SKIP_EXECUTABLES
Create a new optimization pass, strength reduction, which will replace
integer multiplication by a constant power of 2 with an equivalent bit
shift. More changes could be added later.
- Does not duplicate constants
- Adds vector |Concat| utility function to a common test header.
