Align -optimize flags with current compiler releases
We provide a generic wrapper for various backend compilers in charmc, and a flag
-optimize that's meant to provide good optimization settings for any given backend without breaking things. Every new compiler release brings new optimization settings along with it. We haven't necessarily kept up with these releases and the options they bring to the table.
For each compiler in wide use (at least GNU, Intel, XL, PGI, Cray), we should make sure that the flags we pass under
-optimize are appropriate for the most recent few releases, in terms of performance, reliability, and compatibility.