re: toolchain/54703: GCC 8 breaks i386 floppy install

[matthew green <mrg%eterna.com.au@localhost>]

something is wrong with libsa ustarfs.c.  i instrumented 
read512block() a little, and it shows that something has
corrupted ustf->uas_volsize after the first call:

NetBSD/x86 ustarfs Primary Bootstrap
read512block: vda 0 volsize 1466368 vda2vn 0
read512block: vda 512 volsize -8192 vda2vn 0
read512block: vda 1024 volsize -8192 vda2vn 0
read512block: vda 1536 volsize -8192 vda2vn 0
read512block: vda 2048 volsize -8192 vda2vn 0
read512block: vda 2560 volsize -8192 vda2vn 0
read512block: vda 3072 volsize -8192 vda2vn 0
read512block: vda 3584 volsize -8192 vda2vn 0
read512block: vda 4096 volsize -8192 vda2vn 0
read512block: vda 4608 volsize -8192 vda2vn 0
read512block: vda 5120 volsize -8192 vda2vn 0
read512block: vda 5632 volsize -8192 vda2vn 0
read512block: vda 6144 volsize -8192 vda2vn 0
read512block: vda 6656 volsize -8192 vda2vn 0
read512block: vda 7168 volsize -8192 vda2vn 0
read512block: vda 7680 volsize -8192 vda2vn 0
read512block: vda 8192 volsize -8192 vda2vn -1
read512block: vda 8704 volsize -8192 vda2vn -1
read512block: vda 9216 volsize -8192 vda2vn -1
read512block: vda 9728 volsize -8192 vda2vn -1
read512block: vda 10240 volsize -8192 vda2vn -1

Please remove disk 1, insert disk 0, and press return...QEMU 4.1.0 monitor - type 'help' for more information
(qemu) info block


.mrg.