* module/system/vm/assembler.scm (link-debug): If there was no debugging
info, reset the file register to 0 from its default value of 1 before
adding the final row.
* module/system/vm/dwarf.scm (line-prog-scan-to-pc): If we rescanned
from the beginning and still found no source info for this pc, return
#f instead of the default value of the file register (1).
* module/system/vm/dwarf.scm (die-line-prog):
(line-prog-advance, line-prog-scan-to-pc): New public interfaces,
allowing clients to interpret the "statement programs" from
.debug_line DWARF sections.
(<meta>, elf->dwarf-context): Record the bounds of the .debug_line
section.
