If a type was the main variant already, then this code was trying to create it
as a variant type of an null main type, causing newly added debug info checks to
fail.  This caused a crash on dlasrt.f.


git-svn-id: https://llvm.org/svn/llvm-project/dragonegg/trunk@178343 91177308-0d34-0410-b5e6-96231b3b80d8