gdb broken on amd64 or omit-frame-pointer or ???

["Jeffrey W. Baker" <jwbaker@acm.org>]

I was trying to debug a crasher in Firefox, but I keep getting these
bogus stack traces out of gdb:

> #210 0x0062776a2f656d6f in ?? ()
> #211 0x5f6e653d474e414c in ?? ()
> #212 0x382d4654552e5355 in ?? ()
> #213 0x373d53454e494c00 in ?? ()
> #214 0x3d4c564c48530031 in ?? ()
> #215 0x2f3d454d4f480031 in ?? ()
> #216 0x62776a2f656d6f68 in ?? ()
> #217 0x445f454d4f4e4700 in ?? ()

The first 48 levels of the stack are correct, but followed by several
hundred levels of junk.  I this problem caused by build flags in firefox
package, or maybe some bogosity in gdb?  Or some other thing?

-jwb