Rewrite assert to avoid warning when the record element type is byte-sized.

BitstreamWriter asserts that when blob data is written from the record
element vector, each element fits in a byte. However, if the record
elements are specified as a SmallVector of 'char', this causes a warning
from -Wtautological-constant-out-of-range-compare. Fix this by using
llvm::isUInt<8> instead of a plain comparison against 256.

llvm-svn: 181545

llvm/include/llvm/Bitcode/BitstreamWriter.h

@@ -381,7 +381,8 @@ private:
           BlobData = 0;
         } else {
           for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx) {
-            assert(Vals[RecordIdx] < 256 && "Value too large to emit as blob");
+            assert(isUInt<8>(Vals[RecordIdx]) &&
+                   "Value too large to emit as blob");
             WriteByte((unsigned char)Vals[RecordIdx]);
           }
         }