FAIL: test-vasprintf-posix failure on darwin12 cause

[Jack Howarth]

   I have identified the difference between the builds of m4 1.4.16 on darwin11,
which doesn't exhibit the test-vasprintf-posix failure in the m4 testsuite, and
darwin12 which does. The key change in the configure output is...

@@ -210,7 +210,7 @@
 checking whether printf supports 'long double' arguments... yes
 checking whether printf supports infinite 'double' arguments... yes
 checking whether printf supports infinite 'long double' arguments... no
-checking whether printf supports the 'a' and 'A' directives... no
+checking whether printf supports the 'a' and 'A' directives... yes
 checking whether printf supports the 'F' directive... yes
 checking whether printf supports the 'n' directive... yes
 checking whether printf supports the 'ls' directive... yes

So on darwin12 and later, appending gl_cv_func_printf_directive_a=no to the 
configure
options eliminates the test-vasprintf-posix failure. Note that on darwin12, the 
tests in question in config.log looks like...

configure:15360: checking whether printf supports the 'a' and 'A' directives
configure:15447: gcc -o conftest -Os -I/sw/include -L/sw/lib conftest.c  >&5
conftest.c:148:48: warning: data argument not used by format string 
[-Wformat-extra-args]
  if (sprintf (buf, "%a %d", 3.1416015625, 33, 44, 55) < 0
                    ~~~~~~~                    ^
/usr/include/secure/_stdio.h:49:56: note: expanded from macro 'sprintf'
  __builtin___sprintf_chk (str, 0, __darwin_obsz(str), __VA_ARGS__)
                                                       ^
conftest.c:154:49: warning: data argument not used by format string 
[-Wformat-extra-args]
  if (sprintf (buf, "%A %d", -3.1416015625, 33, 44, 55) < 0
                    ~~~~~~~                     ^
/usr/include/secure/_stdio.h:49:56: note: expanded from macro 'sprintf'
  __builtin___sprintf_chk (str, 0, __darwin_obsz(str), __VA_ARGS__)
                                                       ^
conftest.c:161:42: warning: data argument not used by format string 
[-Wformat-extra-args]
  if (sprintf (buf, "%.2a %d", 1.51, 33, 44, 55) < 0
                    ~~~~~~~~~            ^
/usr/include/secure/_stdio.h:49:56: note: expanded from macro 'sprintf'
  __builtin___sprintf_chk (str, 0, __darwin_obsz(str), __VA_ARGS__)
                                                       ^
conftest.c:169:48: warning: data argument not used by format string 
[-Wformat-extra-args]
  if (sprintf (buf, "%010a %d", 1.0 / 0.0, 33, 44, 55) < 0
                    ~~~~~~~~~~                 ^
/usr/include/secure/_stdio.h:49:56: note: expanded from macro 'sprintf'
  __builtin___sprintf_chk (str, 0, __darwin_obsz(str), __VA_ARGS__)
                                                       ^
4 warnings generated.
configure:15447: $? = 0
configure:15447: ./conftest
configure:15447: $? = 0
configure:15458: result: yes

Interetingly, using -D_FORTIFY_SOURCE=0 doesn't seem to suppress the failures
whereas disabling the detection of the printf supports the 'a' and 'A' 
directives
to always be no does.
            Jack