autobuild: Require C++17
autobuild: Require C++17

This completes commit 73a325494e8c8c64f166a86601e3b6ebae4ec608.

Signed-off-by: Stefan Weil <8d4c780fcfdc41841e5070f4c43da8958ba6aec0@weilnetz.de>

amitdo/tesseract,stweil/tesseract,UB-Mannheim/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,UB-Mannheim/tesseract,tesseract-ocr/tesseract,tesseract-ocr/tesseract,stweil/tesseract,UB-Mannheim/tesseract,amitdo/tesseract,stweil/tesseract,tesseract-ocr/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,stweil/tesseract,UB-Mannheim/tesseract,UB-Mannheim/tesseract,amitdo/tesseract,stweil/tesseract