Identify and lower library functions

• Add LibraryCall node for representing opaque library calls.
  • Integrate into collections analysis and GCM to properly track collection flow.
• Add rewrite-math-expressions pass to rewrite einsum reductions into LibraryCall nodes.
• Lower LibraryCall to functions in hercules_rt in RT backend.
• Add wrapper for cublasSgemm.
• Rewrite juno_matmul test on the GPU.

juno_samples/matmul/src/gpu.sch

@@ -24,4 +24,3 @@ dce(*);
 
 float-collections(*);
 gcm(*);
-xdot[true](*);