check for valid location of zero length dwarf block forms?

[Jack Howarth]

   Since the var-tracking-association code merge into
gcc trunk, we have had issues with Apple's dsymutil
program crashing on the code generated by the FSF
gcc trunk compiler...

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41473

Apple's dsymutil maintainer analyzed this issue...

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41473#c27
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41473#c29

...as dwarf debug info containing an AT_location with
any block form having a zero length.
   The question is if these emitted dwarf codes are
accidental errors. Apple believes that if the variable
doesn't have a location, the DW_AT_location attribute
shouldn't be emitted. Also, if the variable does have
a valid location, then the length of zero is likely
a bug in dwarf2out.c.
   It might be worthwhile for the gdb developers to
look into this issue since there might be either
unnecessary dwarf output or incorrect dwarf output
that binutils doesn't recognize as such.
     Thanks in advance for any comments.
                 Jack