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.
The CMAKE_Fortran_DEFINE_FLAG value applies to the IBM Fortran compilers
on all platforms. This moves the setting to the platform-independent
compiler information file.