[flang] Correct file type for .FOR extension

Although not standard, Fortran upper-case extensions generally indicate
files that require preprocessing. This convention holds for most cases
in `clang/lib/Driver/Types.cpp`, except for `.FOR`.

This commit fixes the inconsistency by ensuring `.FOR` files are
correctly identified as `TY_Fortran`, aligning their behavior with other
upper-case Fortran extensions.

Author: inaki-amatria

clang/lib/Driver/Types.cpp

@@ -345,7 +345,7 @@ types::ID types::lookupTypeForExtension(llvm::StringRef Ext) {
       .Case("F95", TY_Fortran)
       .Case("f95", TY_PP_Fortran)
       .Case("for", TY_PP_Fortran)
-      .Case("FOR", TY_PP_Fortran)
+      .Case("FOR", TY_Fortran)
       .Case("fpp", TY_Fortran)
       .Case("FPP", TY_Fortran)
       .Case("gch", TY_PCH)