XL: Fix old VisualAge branding of Fortran compiler
Commit 6d434ee6 (Split XL compiler information files, 2009-09-30)
added Platform/AIX-(XL|VisualAge)-(C|CXX|Fortran).cmake modules
to support the old and new compiler branding for all languages.
Add the "AIX-VisualAge-Fortran" combination that was left out
accidentally.
Brad King