[mpact][external] bump torch-mlir to @6934ab81b0efe105a4800 (#77)

Note that this is actually to get the
bump llvm/llvm-project@b6603e1 so we
can proceed with parallelization
diff --git a/externals/torch-mlir b/externals/torch-mlir
index b3942ff..6934ab8 160000
--- a/externals/torch-mlir
+++ b/externals/torch-mlir
@@ -1 +1 @@
-Subproject commit b3942ff984cdb44e3f5e17194632d0bfc6a613cc
+Subproject commit 6934ab81b0efe105a480063d594d1810fa14b743