The ENABLE_DBG_MSGS flag controls printing of verbose debug messages to
stdout as each SPIR-V instruction is executed. This is very handy for
performing text diffs when the thread count is reduced to 1 and execution
is deterministic.

Bug: b/140287657
Change-Id: I3b62f0f9f3017087cf7f2786e1c30497cfa05a20
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31488Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>