Add the union keyword.

llvm-svn: 97155
diff --git a/llvm/utils/vim/llvm.vim b/llvm/utils/vim/llvm.vim
index 6e4a207..36d78e6 100644
--- a/llvm/utils/vim/llvm.vim
+++ b/llvm/utils/vim/llvm.vim
@@ -57,6 +57,7 @@
 syn keyword llvmKeyword addrspace section alias sideeffect c gc
 syn keyword llvmKeyword target datalayout triple
 syn keyword llvmKeyword blockaddress
+syn keyword llvmKeyword union
 
 " Obsolete keywords.
 syn keyword llvmError  uninitialized implementation