Revert "Merge branch 'issue/cmake-flags-extraction-dunepy' into 'master'"

This reverts merge request !1270 (merged)

The regex is not right. The flags can contain for example the string

'-DCMAKE_CXX_FLAGS=-std=c++17 -Wall -Winit-self -Wfatal-errors -DNDEBUG -O3 -funroll-loops   -finline-functions   -msse3 -mfpmath=sse -mavx2 -maes   -fomit-frame-pointer   -ftree-vectorize    -fdiagnostics-color=always'

which is now abbreviated to the string

'-DCMAKE_CXX_FLAGS=-std=c++17'

This worked correctly previously.