mlir: Add Enzyme ops removal on structured control flow #6669

Job	Run time
Enzyme CI LLVM 15 Release ubuntu-22.04	4m 41s
Enzyme CI LLVM 15 Release macOS	5m 53s
Enzyme CI LLVM 15 Debug ubuntu-22.04	4m 10s
Enzyme CI LLVM 16 Release macOS XCode	2m 40s
Enzyme CI LLVM 15 Debug macOS	2m 34s
Enzyme CI LLVM 16 Release ubuntu-22.04	4m 30s
Enzyme CI LLVM 16 Release macOS	5m 36s
Enzyme CI LLVM 16 Debug ubuntu-22.04	3m 44s
Enzyme CI LLVM 16 Debug macOS	2m 27s
	36m 15s

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