reject invalid comma stuff with a message. We reject the case in

PR6888 with:

$ llvm-as t.ll
llvm-as: t.ll:2:29: error: expected metadata or 'align'
 store <3 x i32> %x, i32 1, i32 1>, <3 x i32>* %p
                            ^

instead of:

$ llvm-as t.ll 
llvm-as: 

llvm-svn: 102154