commit e4043b84c49e1cf9bcf1e8320233343ecc34f8eb
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jun 27 17:12:13 2017 +0000

    Fix strftime build with GCC 8.
    
    Building with current GCC mainline fails with:
    
    strftime_l.c: In function '__strftime_internal':
    strftime_l.c:719:4: error: macro expands to multiple statements [-Werror=multistatement-macros]
        digits = d > width ? d : width;          \
        ^
    strftime_l.c:1260:6: note: in expansion of macro 'DO_NUMBER'
          DO_NUMBER (1, tp->tm_year + TM_YEAR_BASE);
          ^~~~~~~~~
    strftime_l.c:1259:4: note: some parts of macro expansion are not guarded by this 'else' clause
        else
        ^~~~
    
    In fact this particular instance is harmless; the code looks like:
    
              if (modifier == L_('O'))
                goto bad_format;
              else
                DO_NUMBER (1, tp->tm_year + TM_YEAR_BASE);
    
    and because of the goto, it doesn't matter that part of the expansion
    isn't under the "else" conditional.  But it's also clearly bad style
    to rely on that.  This patch changes DO_NUMBER and DO_NUMBER_SPACEPAD
    to use do { } while (0) to avoid such problems.
    
    Tested (full testsuite) for x86_64 (GCC 6), and with
    build-many-glibcs.py with GCC mainline, in conjunction with my libgcc
    patch <https://gcc.gnu.org/ml/gcc-patches/2017-06/msg02032.html>.
    
            * time/strftime_l.c (DO_NUMBER): Define using do { } while (0).
            (DO_NUMBER_SPACEPAD): Likewise.

---
 time/strftime_l.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

--- a/time/strftime_l.c
+++ b/time/strftime_l.c
@@ -715,12 +715,22 @@
       format_char = *f;
       switch (format_char)
 	{
-#define DO_NUMBER(d, v) \
-	  digits = d > width ? d : width;				      \
-	  number_value = v; goto do_number
-#define DO_NUMBER_SPACEPAD(d, v) \
-	  digits = d > width ? d : width;				      \
-	  number_value = v; goto do_number_spacepad
+#define DO_NUMBER(d, v)				\
+	  do					\
+	    {					\
+	      digits = d > width ? d : width;	\
+	      number_value = v;			\
+	      goto do_number;			\
+	    }					\
+	  while (0)
+#define DO_NUMBER_SPACEPAD(d, v)		\
+	  do					\
+	    {					\
+	      digits = d > width ? d : width;	\
+	      number_value = v;			\
+	      goto do_number_spacepad;		\
+	    }					\
+	  while (0)
 
 	case L_('%'):
 	  if (modifier != 0)
