deps: backport e28183b5 from upstream V8

Original commit message:

    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}

PR-URL: #15562
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Steven R Loomis <srloomis@us.ibm.com>

deps/v8/include/v8-version.h

@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 4
 #define V8_MINOR_VERSION 5
 #define V8_BUILD_NUMBER 103
-#define V8_PATCH_LEVEL 49
+#define V8_PATCH_LEVEL 50
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)

deps/v8/src/bignum.cc

@@ -70,7 +70,9 @@ 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;

deps/v8/test/cctest/compiler/test-js-typed-lowering.cc

@@ -217,10 +217,6 @@ 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();
 }