From: Rafal Luzynski <digitalfreak@lingonborough.com>
Date: Sat, 10 Feb 2018 14:07:56 +0100
Subject: calendar: Use the new "%OB" format if supported

Due to the recent changes introduced in glibc 2.27 "%OB" is the
correct format to obtain a month name as used in the calendar
header.  The same rule has been working in BSD family (including
OS X) since 1990s.  This simple hack checks whether "%OB" is supported
at runtime and uses it if it is, falls back to the old "%B" otherwise.

Bug: #9
Origin: upstream, 2.24.33, commit:2ea743ab466703091a44a74e1a4ac7db983c0bca
---
 gtk/gtkcalendar.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/gtk/gtkcalendar.c b/gtk/gtkcalendar.c
index 2dd68d6..28baba1 100644
--- a/gtk/gtkcalendar.c
+++ b/gtk/gtkcalendar.c
@@ -689,6 +689,7 @@ gtk_calendar_init (GtkCalendar *calendar)
 #ifdef G_OS_WIN32
   wchar_t wbuffer[100];
 #else
+  static const char *month_format = NULL;
   char buffer[255];
   time_t tmp_time;
 #endif
@@ -714,7 +715,7 @@ gtk_calendar_init (GtkCalendar *calendar)
       {
 #ifndef G_OS_WIN32
 	tmp_time= (i+3)*86400;
-	strftime ( buffer, sizeof (buffer), "%a", gmtime (&tmp_time));
+	strftime (buffer, sizeof (buffer), "%a", gmtime (&tmp_time));
 	default_abbreviated_dayname[i] = g_locale_to_utf8 (buffer, -1, NULL, NULL, NULL);
 #else
 	if (!GetLocaleInfoW (GetThreadLocale (), LOCALE_SABBREVDAYNAME1 + (i+6)%7,
@@ -730,7 +731,21 @@ gtk_calendar_init (GtkCalendar *calendar)
       {
 #ifndef G_OS_WIN32
 	tmp_time=i*2764800;
-	strftime ( buffer, sizeof (buffer), "%B", gmtime (&tmp_time));
+	if (G_UNLIKELY (month_format == NULL))
+	  {
+	    buffer[0] = '\0';
+	    month_format = "%OB";
+	    strftime (buffer, sizeof (buffer), month_format, gmtime (&tmp_time));
+	    /* "%OB" is not supported in Linux with glibc < 2.27  */
+	    if (!strcmp (buffer, "%OB") || !strcmp (buffer, "OB") || !strcmp (buffer, ""))
+	      {
+		month_format = "%B";
+		strftime (buffer, sizeof (buffer), month_format, gmtime (&tmp_time));
+	      }
+	  }
+	else
+	  strftime (buffer, sizeof (buffer), month_format, gmtime (&tmp_time));
+
 	default_monthname[i] = g_locale_to_utf8 (buffer, -1, NULL, NULL, NULL);
 #else
 	if (!GetLocaleInfoW (GetThreadLocale (), LOCALE_SMONTHNAME1 + i,
