Add an assert.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119788 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index a23bab2..9ca8928 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -499,7 +499,9 @@
     // FIXME: It is probably better if we don't call EvaluateAsAbsolute in
     // here.
     int64_t Value;
-    LF.getValue().EvaluateAsAbsolute(Value, &Layout);
+    bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, &Layout);
+    assert(IsAbs);
+    (void) IsAbs;
     SmallString<32> Tmp;
     raw_svector_ostream OSE(Tmp);
     if (LF.isSigned())