libstdc++: Avoid bad_alloc exceptions when changing locales

For the --enable-clocale=generic configuration, the current code can
fail with a bad_alloc exception. This patch uses the nothrow version of
operator new and reports allocation failures by setting failbit in the
iostate variable.

	* config/locale/generic/c_locale.cc (__set_C_locale()): New function
	to set the "C" locale and return the name of the previous locale.
	(__convert_to_v<float>, __convert_to_v<double>)
	(__convert_to_v<long double>): Use __set_C_locale and set failbit on
	error.

libstdc++-v3/config/locale/generic/c_locale.cc

@@ -52,6 +52,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ~_Save_errno() { if (errno == 0) errno = _M_errno; }
       int _M_errno;
     };
+
+    // calls setlocale(LC_ALL, "C") and returns a string containing the old
+    // locale name. Caller must delete[] the string. Returns NULL on error.
+    const char*
+    __set_C_locale()
+    {
+      char* __old = setlocale(LC_ALL, 0);
+      const size_t __len = strlen(__old) + 1;
+      char* __sav = new(nothrow) char[__len];
+      if (__sav)
+	{
+	  memcpy(__sav, __old, __len);
+	  setlocale(LC_ALL, "C");
+	}
+      return __sav;
+    }
   }
 
   template<>
@@ -60,11 +76,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		   const __c_locale&) throw()
     {
       // Assumes __s formatted for "C" locale.
-      char* __old = setlocale(LC_ALL, 0);
-      const size_t __len = strlen(__old) + 1;
-      char* __sav = new char[__len];
-      memcpy(__sav, __old, __len);
-      setlocale(LC_ALL, "C");
+      const char* __sav = __set_C_locale();
+      if (!__sav)
+	{
+	  __err = ios_base::failbit;
+	  return;
+	}
       char* __sanity;
       bool __overflow = false;
 
@@ -125,11 +142,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		   const __c_locale&) throw()
     {
       // Assumes __s formatted for "C" locale.
-      char* __old = setlocale(LC_ALL, 0);
-      const size_t __len = strlen(__old) + 1;
-      char* __sav = new char[__len];
-      memcpy(__sav, __old, __len);
-      setlocale(LC_ALL, "C");
+      const char* __sav = __set_C_locale();
+      if (!__sav)
+	{
+	  __err = ios_base::failbit;
+	  return;
+	}
       char* __sanity;
 
 #if !__DBL_HAS_INFINITY__
@@ -170,11 +188,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		   ios_base::iostate& __err, const __c_locale&) throw()
     {
       // Assumes __s formatted for "C" locale.
-      char* __old = setlocale(LC_ALL, 0);
-      const size_t __len = strlen(__old) + 1;
-      char* __sav = new char[__len];
-      memcpy(__sav, __old, __len);
-      setlocale(LC_ALL, "C");
+      const char* __sav = __set_C_locale();
+      if (!__sav)
+	{
+	  __err = ios_base::failbit;
+	  return;
+	}
 
 #if !__LDBL_HAS_INFINITY__
       const _Save_errno __save_errno;