fix: don't try to use a cross-architecture objdump on the native arch…

[pcc]

…itecture

If the host architecture is aarch64, aarch64-linux-gnu-objdump may not exist, which is the case on at least Fedora and NixOS, so disassembly doesn't work by default. Similar logic likely also applies to arm-linux-gnueabi-objdump. Fix the problem by only trying to use the cross-architecture objdump if we are not building for the given architecture.