[gcc r11-5495] libstdc++: Partially revert r11-5314

[gcc r11-5495] libstdc++: Partially revert r11-5314

[Jonathan Wakely]

https://gcc.gnu.org/g:0d7d69ca4a8c05d883e07ee42058c9c6b0c72370

commit r11-5495-g0d7d69ca4a8c05d883e07ee42058c9c6b0c72370
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 27 11:00:15 2020 +0000

    libstdc++: Partially revert r11-5314
    
    The changes in r11-5314 are broken, because it means we don't use
    __gthread_once for the first few initializations, but after the program
    becomes multi-threaded we will repeat the initialization, using
    __gthread_once once this time. This leads to memory errors.
    
    The use of __is_single_threaded() in locale::id::_M_id() is OK, because
    the side effects are the same either way.
    
    libstdc++-v3/ChangeLog:
    
            * src/c++98/locale.cc (locale::facet::_S_get_c_locale()):
            Revert change to use __is_single_threaded.
            * src/c++98/locale_init.cc (locale::_S_initialize()):
            Likewise.

Diff:
---
 libstdc++-v3/src/c++98/locale.cc      | 2 +-
 libstdc++-v3/src/c++98/locale_init.cc | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/src/c++98/locale.cc b/libstdc++-v3/src/c++98/locale.cc
index 9b3fc351515..4c1612cc5dc 100644
--- a/libstdc++-v3/src/c++98/locale.cc
+++ b/libstdc++-v3/src/c++98/locale.cc
@@ -214,7 +214,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   locale::facet::_S_get_c_locale()
   {
 #ifdef __GTHREADS
-    if (!__gnu_cxx::__is_single_threaded())
+    if (__gthread_active_p())
       __gthread_once(&_S_once, _S_initialize_once);
     else
 #endif
diff --git a/libstdc++-v3/src/c++98/locale_init.cc b/libstdc++-v3/src/c++98/locale_init.cc
index fc8416ba01a..c3841ccbd3c 100644
--- a/libstdc++-v3/src/c++98/locale_init.cc
+++ b/libstdc++-v3/src/c++98/locale_init.cc
@@ -320,7 +320,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   locale::_S_initialize()
   {
 #ifdef __GTHREADS
-    if (!__gnu_cxx::__is_single_threaded())
+    if (__gthread_active_p())
       __gthread_once(&_S_once, _S_initialize_once);
 #endif
     if (!_S_classic)