Auto merge of #2730 - alexcrichton:fix-panic-abort-build-script, r=alexcrichton

Fix build scripts and panic=abort

Build scripts were apparently always compiled with the "dev" profile rather than
the standard "match whatever the normal build was" profile, which meant that if
dev/release disagreed on panic=abort you'd get compile errors. Seems bad!

This commit fixes this by just having build scripts always compile with the same
profile as libraries (for now), as this was the original intention anyway.

Closes #2726