Fix gcc line in Makefile for Linux

[fdmarcin]

I needed this change for make to succeed on Fedora 41. Not sure if this is the right way to do this, so I'm open to suggestions. I haven't tested this on other Linux distros.

As it is currently on master, I've been getting this error when trying to run make:

cgo: C compiler "x86_64-linux-gnu-gcc" not found: exec: "x86_64-linux-gnu-gcc": executable file not found in $PATH

[fdmarcin]

@norio-nomura Hi! You were the last one to rewrite that section of the Makefile. I've no idea if my changes are correct. Would you mind taking a look? 🙇

[fdmarcin]

Alright, release fails, so this is probably not the right way to fix this. I'll leave this open, but if the maintainers don't have another idea, this can be closed.

[jandubois]

compiler "x86_64-linux-gnu-gcc" not found: exec: "x86_64-linux-gnu-gcc": executable file not found in $PATH

Did you trying installing the gcc-x86_64-linux package (it is a subpackage of cross-gcc)?

Your change is breaking cross-compilation, so I think this issue should be closed.

[afbjorklund]

I don't think that we need to use the cross-compiler for the local build, only for the actual cross...

In the same way we don't need to set GOOS and GOARCH either, but just call out to go build.

It was just something that came with the caching and performance optimizations of the Makefile.