Suppress defaulting warnings from cryptol.

[brianhuffman]

This incorporates GaloisInc/saw-core#70, which suppresses the
defaulting warning messages upon loading cryptol modules.

Fixes #768.

[brianhuffman]

I had forgotten that some of the changes from GaloisInc/saw-core#69 will need changes to saw-script, to avoid ambiguous references after moving a couple of functions from saw-script into cryptol-saw-core. I'll need to make a PR for that first before we merge this one.

[brianhuffman]

I just rebased on top of #821, so now it should work.

[brianhuffman]

The ghc-8.8.3 macos build is failing with this error:

<command line>: dlopen(/Users/runner/work/saw-script/saw-script/dist-newstyle/build/x86_64-osx/ghc-8.8.3/llvm-pretty-0.10.3/build/libHSllvm-pretty-0.10.3-inplace-ghc8.8.3.dylib, 5): no suitable image found.  Did find:
	/Users/runner/work/saw-script/saw-script/dist-newstyle/build/x86_64-osx/ghc-8.8.3/llvm-pretty-0.10.3/build/libHSllvm-pretty-0.10.3-inplace-ghc8.8.3.dylib: unknown file type, first eight bytes: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
	/Users/runner/work/saw-script/saw-script/dist-newstyle/build/x86_64-osx/ghc-8.8.3/llvm-pretty-0.10.3/build/libHSllvm-pretty-0.10.3-inplace-ghc8.8.3.dylib: unknown file type, first eight bytes: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
cabal: Failed to build crucible-llvm-0.3 (which is required by
saw-script-0.4.0.99).

The command has failed after 3 attempts.
##[error]Process completed with exit code 1.

I don't see how this failure could possibly be caused by this PR; can anyone explain it?

[brianhuffman]

I restarted the CI tests and they failed again in exactly the same way.

[brianhuffman]

The failing CI checks are not marked as "required", so I'm going to go ahead and merge anyway.