[turbofan] Fix more -Wsign-compare warnings.

src/arm/assembler-arm.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 1567 matching lines @@
   // Resume constant pool emission. Need to be called as many time as
   // StartBlockConstPool to have an effect.
   void EndBlockConstPool() {
     if (--const_pool_blocked_nesting_ == 0) {
 #ifdef DEBUG
       // Max pool start (if we need a jump and an alignment).
       int start = pc_offset() + kInstrSize + 2 * kPointerSize;
       // 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
       // Two cases:
       //  * no_const_pool_before_ >= next_buffer_check_ and the emission is
       //    still blocked
       //  * no_const_pool_before_ < next_buffer_check_ and the next emit will
       //    trigger a check.
       next_buffer_check_ = no_const_pool_before_;
     }
@@ skipping 109 matching lines @@
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARM_ASSEMBLER_ARM_H_