Fix compilation with GCC 5.2

Fixes:

../../test/cctest/compiler/test-js-typed-lowering.cc:224:14:
 error: ‘kJSTypes’ defined but not used [-Werror=unused-variable]
  static Type* kJSTypes[] = {Type::Undefined(), Type::Null(),   Type::Boolean(),

../../src/bignum.cc: In member function
 ‘void v8::internal::Bignum::AssignDecimalString(Vector<const char>)’:
  ../../src/bignum.cc:80:6: error: assuming signed overflow does not occur when
  assuming that (X + c) < X is always false [-Werror=strict-overflow]

../../src/compiler/ia32/code-generator-ia32.cc:1366:3:
  required from here ../../src/base/logging.h:123:26:
   error: comparison between signed and unsigned integer expressions
   [-Werror=sign-compare] DEFINE_CHECK_OP_IMPL(EQ, ==)

BUG=

Review URL: https://codereview.chromium.org/1371823002

Cr-Commit-Position: refs/heads/master@{#31095}

src/bignum.cc

@@ -68,7 +68,9 @@ static uint64_t ReadUInt64(Vector<const char> buffer,
                            int from,
                            int digits_to_read) {
   uint64_t result = 0;
-  for (int i = from; i < from + digits_to_read; ++i) {
+  int to = from + digits_to_read;
+
+  for (int i = from; i < to; ++i) {
     int digit = buffer[i] - '0';
     DCHECK(0 <= digit && digit <= 9);
     result = result * 10 + digit;

src/compiler/ia32/code-generator-ia32.cc

@@ -1363,7 +1363,7 @@ void CodeGenerator::AssembleReturn() {
   }
   size_t pop_size = descriptor->StackParameterCount() * kPointerSize;
   // Might need ecx for scratch if pop_size is too big.
-  DCHECK_EQ(0, descriptor->CalleeSavedRegisters() & ecx.bit());
+  DCHECK_EQ(0u, descriptor->CalleeSavedRegisters() & ecx.bit());
   __ Ret(static_cast<int>(pop_size), ecx);
 }
 

src/compiler/x64/code-generator-x64.cc

@@ -1618,7 +1618,7 @@ void CodeGenerator::AssembleReturn() {
   }
   size_t pop_size = descriptor->StackParameterCount() * kPointerSize;
   // Might need rcx for scratch if pop_size is too big.
-  DCHECK_EQ(0, descriptor->CalleeSavedRegisters() & rcx.bit());
+  DCHECK_EQ(0u, descriptor->CalleeSavedRegisters() & rcx.bit());
   __ Ret(static_cast<int>(pop_size), rcx);
 }
 

test/cctest/compiler/test-js-typed-lowering.cc

@@ -219,10 +219,6 @@ static Type* kNumberTypes[] = {
     Type::OrderedNumber(), Type::PlainNumber(), Type::Number()};
 
 
-static Type* kJSTypes[] = {Type::Undefined(), Type::Null(),   Type::Boolean(),
-                           Type::Number(),    Type::String(), Type::Object()};
-
-
 static Type* I32Type(bool is_signed) {
   return is_signed ? Type::Signed32() : Type::Unsigned32();
 }