Workaround restrict error in GCC 12

https://bugs.webkit.org/show_bug.cgi?id=272309

Reviewed by Darin Adler.

In GCC 12.3.0:

In static member function ‘static constexpr std::char_traits<char>::char_type* std::char_traits<char>::copy(char_type*, const char_type*, std::size_t)’,
    inlined from ‘static constexpr void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy(_CharT*, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:431:21,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits, _Allocator>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_replace(size_type, size_type, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.tcc:532:22,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::replace(size_type, size_type, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:2179:19,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::insert(size_type, const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:1936:22,
    inlined from ‘std::ostream& WTF::operator<<(std::ostream&, Int128Impl)’ at /host/home/tingping/Projects/WebKit/Source/WTF/wtf/Int128.cpp:268:17:
/usr/include/c++/12/bits/char_traits.h:435:56: error: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ accessing 9223372036854775810 or more bytes at offsets [2, 9223372036854775807] and 1 may overlap up to 9223372036854775813 bytes at offset -3 [-Werror=restrict]
  435 |         return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n));
      |                                        ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~

* Source/WTF/wtf/Int128.cpp:
(WTF::operator<<):

Canonical link: https://commits.webkit.org/277203@main

Source/WTF/wtf/Int128.cpp

@@ -265,9 +265,9 @@ std::ostream& operator<<(std::ostream& os, Int128Impl v) {
       (flags & std::ios::basefield) == std::ios_base::fmtflags();
   if (print_as_decimal) {
     if (Int128High64(v) < 0) {
-      rep = "-";
+      rep.append("-");
     } else if (flags & std::ios::showpos) {
-      rep = "+";
+      rep.append("+");
     }
   }