/usr/lib/R/site-library/fRegression/obsolete/src/Makevars is in r-cran-fregression 3011.81-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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PKG_LIBS=$(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)