[llvm] [CodeGen] Port MachineCFGPrinter to new pass manager (PR #137570)

[Matt Arsenault via llvm-commits]

================
@@ -2,6 +2,10 @@
 # RUN: FileCheck %s -input-file=%t.irreducible.dot --check-prefix=MCFG
 # RUN: llc -mtriple=amdgcn-- -run-pass=dot-machine-cfg  -mcfg-dot-filename-prefix=%t -dot-mcfg-only -o -  %s 2>&1 > /dev/null
 # RUN: FileCheck %s -input-file=%t.irreducible.dot --check-prefix=MCFG-ONLY
+# RUN: llc -mtriple=amdgcn-- -passes=dot-machine-cfg  -mcfg-dot-filename-prefix=%t -o -  %s 2>&1 > /dev/null
----------------
arsenm wrote:

Very roundabout way of discarding both stdout and stderr. Should probably check something is printed 

https://github.com/llvm/llvm-project/pull/137570