OPUS: Fix DTX detection #4559

Job	Run time
ci (ubuntu-20.04, gcc, g++, 20, Release)	7m 42s
ci (ubuntu-20.04, gcc, g++, 20, Debug)	7m 3s
ci (ubuntu-20.04, clang, clang++, 20, Release)	8m 3s
ci (ubuntu-20.04, clang, clang++, 20, Debug)	6m 57s
ci (ubuntu-22.04, gcc, g++, 20, Release)	7m 19s
ci (ubuntu-22.04, gcc, g++, 20, Debug)	6m 25s
ci (ubuntu-22.04, clang, clang++, 20, Release)	8m 42s
ci (ubuntu-22.04, clang, clang++, 20, Debug)	7m 52s
ci (macos-12, gcc, g++, 20, Release)	10m 42s
ci (macos-12, gcc, g++, 20, Debug)	6m 28s
ci (macos-14, clang, clang++, 20, Release)	3m 59s
ci (macos-14, clang, clang++, 20, Debug)	3m 40s
ci (windows-2022, cl, cl, 20, Release)	6m 49s
ci (windows-2022, cl, cl, 20, Debug)	5m 44s
	1h 37m 25s

Provide feedback