We create appropriate ELF files automatically based on GOOS. There's
no point in supporting -H elf flag, particularly since we need to emit
different flavors of ELF depending on GOOS anyway.
If that weren't reason enough, -H elf appears to be broken since at
least Go 1.4. At least I wasn't able to find a way to make use of it.
As best I can tell digging through commit history, -H elf is just an
artifact leftover from Plan 9's 6l linker.