stage2.Elf: fix off by one error in writeOffsetTableEntry
stage2.Elf: fix off by one error in writeOffsetTableEntry

The code was using the length of the local symbols, which also
includes the null symbol. Fix this by using the offset table instead,
which only keeps track of the symbols that end up in the got.

raulgrell/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig