cmd/link: dynamic symbols in 386 ELF have a zero size

[4a6f656c]

When generating 386 ELF, the Go linker emits dynamic symbols that have a size of zero, even though the symbol in the symbol table has the correct size:

$ objdump -t ./go | grep __progname
086755a0 g O .noptrbss 00000004 __progname
$ objdump -T ./go | grep __progname
086755a0 g DO .text 00000000 __progname

This can cause potential issues (or at least warnings) with dynamic linking.

[gopherbot]

CL https://golang.org/cl/22912 mentions this issue.