[libpostal] add build script for libpostal

[mattwigway]

This adds a build script for libpostal, an address-parsing library. I intend to write a Julia wrapper for it (WIP at mattwigway/Postal.jl).

I do have two questions about how to package this:

1. libpostal doesn't really follow a versioning scheme; the last release was seven years ago and everyone seems to just use master. I'm not sure how to version the JLL.
2. I'm getting a warning about the binaries using avx2 instructions on the w64 builds. I tried adding -mno-avx2 to CFLAGS but that didn't solve the problem, I'm not sure what else to try.

[imciner2]

I'm getting a warning about the binaries using avx2 instructions on the w64 builds. I tried adding -mno-avx2 to CFLAGS but that didn't solve the problem, I'm not sure what else to try.

You can safely ignore this probably. The auditor seems to always give that warning, even in cases where no problematic instructions are present.

[imciner2]

I see in the artifact that it includes libpostal.a, which is the static library. We generally don't like to include static libraries in the JLL packages (unless absolutely necessary) because they bloat the storage and download sizes of the packages and the end users don't ever need them. I'd suggest disabling the static library build.

[mattwigway]

@imciner2 should be fixed, thanks!

[mattwigway]

@giordano sure enough, thanks for the tip! Fixed now and the build works for aarch64-linux