Update the IPO support for GCC and CLANG.

Note that you may need to define "AR", "LD" and "RANLIB", if the names do not match the default ones (clang/llvm are often trailed by version numbers).

Fixes #539 (closed)

Try these out.

Excellent, thanks! Works perfectly.

Good, may as well merge away.

merged

mentioned in commit fb7f71e1