CONFIGURE: Never enable release_build by default.

This changes the default for Caanoo, GP2x, GP2xWiz, OpenPandora and PS2.
For those now we only disable debug symbols and enable optimizations by
default.
CONFIGURE: Use -O3 for OpenPandora when optimizations are requested.

Formerly -O3 was only used for release builds.
Merge pull request #304 from lordhoto/configure-no-release-default

CONFIGURE: Never enable release_build by default.