[turbofan] Fix more -Wsign-compare warnings.

src/arm/assembler-arm.h

Index: src/arm/assembler-arm.h
diff --git a/src/arm/assembler-arm.h b/src/arm/assembler-arm.h
index e5448f79aeb34d9ce24e07cb0f8582317c6d9e8b..96b33be4acf3c1fccf251a7d7dfd40ff0b4d99fa 100644
--- a/src/arm/assembler-arm.h
+++ b/src/arm/assembler-arm.h
@@ -1585,7 +1585,8 @@ class Assembler : public AssemblerBase {
       // Check the constant pool hasn't been blocked for too long.
       DCHECK(pending_32_bit_constants_.empty() ||
              (start + pending_64_bit_constants_.size() * kDoubleSize <
-              (first_const_pool_32_use_ + kMaxDistToIntPool)));
+              static_cast<size_t>(first_const_pool_32_use_ +
+                                  kMaxDistToIntPool)));
       DCHECK(pending_64_bit_constants_.empty() ||
              (start < (first_const_pool_64_use_ + kMaxDistToFPPool)));
 #endif