[libcxx] Check return value for asprintf()

[brad]

Summary

Submitting upstream from OpenBSD tree:

local __libcpp_asprintf_l() -> libc asprintf() was inspecting the pointer (with indeterminate value) for failure, rather than the return value of -1.

[ldionne]

Please fix the CI issues and ping again if you'd like to get this reviewed.

[brad]

Fix the comparison between signed and unsigned values.

[ldionne]

LGTM, thanks!

libcxx/include/locale

         __nc = __libcpp_snprintf_l(__nb, __nbuf, _LIBCPP_GET_C_LOCALE, __fmt, __v);
     unique_ptr<char, void(*)(void*)> __nbh(nullptr, free);
     if (__nc > static_cast<int>(__nbuf-1))
     {
         if (__specify_precision)
             __nc = __libcpp_asprintf_l(&__nb, _LIBCPP_GET_C_LOCALE, __fmt, (int)__iob.precision(), __v);
         else
             __nc = __libcpp_asprintf_l(&__nb, _LIBCPP_GET_C_LOCALE, __fmt, __v);
-        if (__nb == nullptr)
+        if (__nc == -1)
             __throw_bad_alloc();
         __nbh.reset(__nb);
     }
     char* __ne = __nb + __nc;
     char* __np = this->__identify_padding(__nb, __ne, __iob);
     // Stage 2 - Widen __nar while adding thousands separators
     char_type __o[2*(__nbuf-1) - 1];
     char_type* __ob = __o;

         __nc = __libcpp_snprintf_l(__nb, __nbuf, _LIBCPP_GET_C_LOCALE, __fmt, __v);
     unique_ptr<char, void(*)(void*)> __nbh(nullptr, free);
     if (__nc > static_cast<int>(__nbuf-1))
     {
         if (__specify_precision)
             __nc = __libcpp_asprintf_l(&__nb, _LIBCPP_GET_C_LOCALE, __fmt, (int)__iob.precision(), __v);
         else
             __nc = __libcpp_asprintf_l(&__nb, _LIBCPP_GET_C_LOCALE, __fmt, __v);
-        if (__nb == nullptr)
+        if (__nc == -1)
             __throw_bad_alloc();
         __nbh.reset(__nb);
     }
     char* __ne = __nb + __nc;
     char* __np = this->__identify_padding(__nb, __ne, __iob);
     // Stage 2 - Widen __nar while adding thousands separators
     char_type __o[2*(__nbuf-1) - 1];
     char_type* __ob = __o;

     char_type* __db = __digits;
     size_t __n = static_cast<size_t>(snprintf(__bb, __bs, "%.0Lf", __units));
     unique_ptr<char, void(*)(void*)> __hn(nullptr, free);
     unique_ptr<char_type, void(*)(void*)> __hd(0, free);
     // secure memory for digit storage
     if (__n > __bs-1)
     {
         __n = static_cast<size_t>(__libcpp_asprintf_l(&__bb, _LIBCPP_GET_C_LOCALE, "%.0Lf", __units));
-        if (__bb == nullptr)
+        if (__n == -1)
             __throw_bad_alloc();
         __hn.reset(__bb);
         __hd.reset((char_type*)malloc(__n * sizeof(char_type)));
         if (__hd == nullptr)
             __throw_bad_alloc();
         __db = __hd.get();
     }
     // gather info