build-sys: make the crosscompile path for scanf_cv_alloc_modifier clever

My earlier assumption was that scanf_cv_alloc_modifier is unused. This
is not true as pointed out by Karel since it used befoe checking for
libmount. Argh. So instead saying no I add a test to check for glibc
>= 2.7 which provides %m. As of uClibc v0.9.32-rc3 the situation looks
the following:
| git grep _M_SPEC__
|libc/stdio/_vfprintf.c:/* #define __UCLIBC_HAS_PRINTF_M_SPEC__ */
|libc/stdio/_vfprintf.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/_vfprintf.c:# ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/_vfprintf.c:# endif /* __UCLIBC_HAS_PRINTF_M_SPEC__ */
|libc/stdio/_vfprintf.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/_vfprintf.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/_vfprintf.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/_vfprintf.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/old_vfprintf.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__
|libc/stdio/perror.c:#ifdef __UCLIBC_HAS_PRINTF_M_SPEC__

And other libc user have to bring their own stuff.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

diff --git a/configure.ac b/configure.ac
index c7ebd4123d1bed5aa24598dc6f8f17e2b139da83..0ae5b767d52c198c51217c08abe06f82a12adebc 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -387,7 +387,23 @@ AC_CACHE_VAL([scanf_cv_alloc_modifier],
       [scanf_cv_alloc_modifier=no]
     )
     ,
-    [scanf_cv_alloc_modifier=no]
+
+    [AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+     #include <stdio.h>
+
+     #ifdef __GLIBC__
+
+     #if !(__GLIBC_PREREQ(2, 7))
+     #error %m is not available
+     #endif
+
+     #else
+
+     #error Your C-library is not supported.
+     #endif
+     ])],
+    [scanf_cv_alloc_modifier=ms],
+    [scanf_cv_alloc_modifier=no])]
   )
 )