[gcc(refs/users/wschmidt/heads/builtins3)] libstdc++: Check _GLIBCXX_USE_C99_STDLIB for strtof and strtold

[William Schmidt <wschmidt@gcc.gnu.org>]

https://gcc.gnu.org/g:e513e9aa53121e628e0403438a5bb3861a50c198

commit e513e9aa53121e628e0403438a5bb3861a50c198
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jul 30 20:55:56 2020 +0100

    libstdc++: Check _GLIBCXX_USE_C99_STDLIB for strtof and strtold
    
    On broken systems we only have strtod, not strtof and strtold. Just use
    strtod for all types, even though that will produce incorrect results in
    some cases.
    
    Similarly, if _GLIBCXX_USE_C99_MATH is not defined then std::isinf won't
    be declared. Just refer to it unqualified, which should find the C
    library's isinf macro if that hasn't been #undef'd by <cmath>.
    
    libstdc++-v3/ChangeLog:
    
            * src/c++17/floating_from_chars.cc (from_chars_impl): Use
            isinf unqualified.
            [!_GLIBCXX_USE_C99_STDLIB]: Use strtod for float and long
            double.

Diff:
---
 libstdc++-v3/src/c++17/floating_from_chars.cc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/src/c++17/floating_from_chars.cc b/libstdc++-v3/src/c++17/floating_from_chars.cc
index f1519e5c7b6..26b69a38521 100644
--- a/libstdc++-v3/src/c++17/floating_from_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_from_chars.cc
@@ -300,12 +300,16 @@ namespace
 	errno = 0;
 	char* endptr;
 	T tmpval;
+#if _GLIBCXX_USE_C99_STDLIB
 	if constexpr (is_same_v<T, float>)
 	  tmpval = std::strtof(str, &endptr);
-	if constexpr (is_same_v<T, double>)
+	else if constexpr (is_same_v<T, double>)
 	  tmpval = std::strtod(str, &endptr);
 	else if constexpr (is_same_v<T, long double>)
 	  tmpval = std::strtold(str, &endptr);
+#else
+	tmpval = std::strtod(str, &endptr);
+#endif
 	const int conv_errno = std::__exchange(errno, save_errno);
 
 #if _GLIBCXX_USE_C99_FENV_TR1
@@ -319,7 +323,7 @@ namespace
 	const ptrdiff_t n = endptr - str;
 	if (conv_errno == ERANGE) [[unlikely]]
 	  {
-	    if (std::isinf(tmpval)) // overflow
+	    if (isinf(tmpval)) // overflow
 	      ec = errc::result_out_of_range;
 	    else // underflow (LWG 3081 wants to set value = tmpval here)
 	      ec = errc::result_out_of_range;