Set some tests to an unknown vendor and OS

This avoids llc using the hosts OS/vendor as defaults and triggering
unwanted behaviour in the tests. This should deal with the buildbot
breakages on windows after r283140.

llvm-svn: 283149
diff --git a/llvm/test/CodeGen/Mips/tls16.ll b/llvm/test/CodeGen/Mips/tls16.ll
index 349e381..8ab7416 100644
--- a/llvm/test/CodeGen/Mips/tls16.ll
+++ b/llvm/test/CodeGen/Mips/tls16.ll
@@ -1,4 +1,4 @@
-; RUN: llc  -march=mipsel -mattr=mips16 -relocation-model=pic -O3 < %s | FileCheck %s -check-prefix=PIC16
+; RUN: llc  -mtriple=mipsel-- -mattr=mips16 -relocation-model=pic -O3 < %s | FileCheck %s -check-prefix=PIC16
 
 @a = thread_local global i32 4, align 4