A source line with a <TAB> character anywhere in it is treated as
entirely significant--however long it is--instead of ending in
column 72 (for fixed-form source) or 132 (for free-form source).
This also is different from f2c, which encodes tabs as
\t (the ASCII <TAB> character) inside character
and Hollerith constants, but nevertheless seems to treat the column
position as if it had been affected by the canonical tab positioning.
g77 effectively
translates tabs to the appropriate number of spaces (a la the default
for the UNIX expand command) before doing any other processing, other
than (currently) noting whether a tab was found on a line and using this
information to decide how to interpret the length of the line and continued
constants.