turn an assert into a proper check, fixing crash on invalid here:

turn an assert into a proper check, fixing crash on invalid here:

$ llvm-as t.ll
llvm-as: t.ll:1:6: error: expected 'type' after '='
%0 = = type { i32, float, float, double }
     ^

PR6810.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100934 91177308-0d34-0410-b5e6-96231b3b80d8