gas buffer overflow with --listing-rhs-width

With listings enabled, gas keeps a small cache of source lines.  They
are stored in buffers of size LISTING_RHS_WIDTH, ie. 100.  Given
listing-rhs-width larger than 100 it is of course possible to overflow
the buffer.  Fix that by allocating as needed.  We could allocate all
buffers on the first call to print_source using listing_rhs_width, but
I chose not to do that in case some future assembly directive allows
changes to listing_rhs_width similarly to the way paper_width can
change during assembly.
1 file changed