More reproduceable hpkg checksums

[kallisti5]

Haiku packages are not reproducible.

(If I build vim-7.2-1-x86_64.hpkg twice, the checksum will wildly vary each time.)

There are places however we could greatly improve the reproducibility however, one example is patching gcc2 to stop putting timestamps in all object files it generates.

The more reproducible hpkg files are when built, the more Haiku could potentially leverage de-duplication and similar tech to reduce the storage size of repositories, and increase the ability for p2p hosting of them.

[kallisti5]

I should note, 100% reproducible builds are unlikely. The goal here is to make them "more reproducible" where some chunk dedup would be beneficial.