Default gcc is gcc-11 (CUDA/torch R14 pin) but the only gfortran is 12,
whose libgfortran-12-dev puts the unversioned libgfortran.so only in the
gcc-12 dir. R links shared objects with gcc-11 + -lgfortran, so the whole
Fortran dependency chain (quadprog/tseries/RcppArmadillo -> soundgen) failed
'cannot find -lgfortran'. Adds an idempotent step installing libgfortran-11-dev
(guarded on 'gcc -print-file-name=libgfortran.so' not resolving). Additive;
default toolchain untouched.
vh
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