Add scan for IBM and Cray mainframe fp formats.

Add scan for IBM and Cray mainframe fp formats.

For completeness: it's quite unlikely Perl would build in those
environments.

Though with Cray it's less impossible: Perl used to build in C90
UNICOS, in 5.8-ish timeframe.

With IBM, highly unlikely, because there probably never was a UNIXy
enough environment where the IBM Floating Point Architecture was used.