This prevents the test from failing if the only thing not supported is
the text printed to the log about the size of the floating-point type.
libstdc++-v3/ChangeLog:
* testsuite/20_util/from_chars/4.cc: Only use log2 if C99 math
functions are available.
(cherry picked from commit
30aea28bd30027e0a6be8e3077828256779954b3)
if (Float_limits::is_iec559 && Float_limits::digits < UInt_limits::digits)
{
+#ifdef _GLIBCXX_USE_C99_MATH_TR1
std::printf("Testing %d-bit float, using %zu-bit integer\n",
Float_limits::digits + (int)std::log2(Float_limits::max_exponent) + 1,
sizeof(UIntT) * __CHAR_BIT__);
+#endif
std::from_chars_result res;
FloatT flt;