package/sane-backends: fix uclibc compile due o missing stdarg.h include

package/sane-backends: fix uclibc compile due o missing stdarg.h include

Add missing stdarg.h include for va_list/va_start/va_end.

Fixes:

  - http://autobuild.buildroot.net/results/88f4ea971875b1a5eb88662326d9343341eaaea2

  microtek.c: In function ‘MDBG_INIT’:
  microtek.c:163:3: error: unknown type name ‘va_list’
    163 |   va_list ap;
        |   ^~~~~~~
  microtek.c:78:1: note: ‘va_list’ is defined in header ‘<stdarg.h>’; did you forget to ‘#include <stdarg.h>’?
     77 | #include "microtek.h"
    +++ |+#include <stdarg.h>
     78 |
  microtek.c:164:3: warning: implicit declaration of function ‘va_start’; did you mean ‘sane_start’? [-Wimplicit-function-declaration]
    164 |   va_start(ap, format);
        |   ^~~~~~~~
        |   sane_start
  microtek.c:165:54: warning: passing argument 4 of ‘vsnprintf’ makes pointer from integer without a cast [-Wint-conversion]
    165 |   vsnprintf(_mdebug_string, MAX_MDBG_LENGTH, format, ap);
        |                                                      ^~
        |                                                      |
        |                                                      int
  In file included from ../include/sane/sanei_config.h:50,
                   from microtek.c:70:
  .../host/x86_64-buildroot-linux-uclibc/sysroot/usr/include/stdio.h:359:57: note: expected ‘__va_list_tag *’ but argument is of type ‘int’
    359 |         const char *__restrict __format, __gnuc_va_list __arg)
        |                                          ~~~~~~~~~~~~~~~^~~~~
  microtek.c:166:3: warning: implicit declaration of function ‘va_end’ [-Wimplicit-function-declaration]
    166 |   va_end(ap);
        |   ^~~~~~

and

  sm3600-scanutil.c: In function ‘debug_printf’:
  sm3600-scanutil.c:69:3: error: unknown type name ‘va_list’
     69 |   va_list ap;
        |   ^~~~~~~
  sm3600-scanutil.c:48:1: note: ‘va_list’ is defined in header ‘<stdarg.h>’; did you forget to ‘#include <stdarg.h>’?
     47 | #include "sm3600-scantool.h"
    +++ |+#include <stdarg.h>
     48 |
  sm3600-scanutil.c:75:3: warning: implicit declaration of function ‘va_start’; did you mean ‘sane_start’? [-Wimplicit-function-decla
ration]
     75 |   va_start(ap,szFormat);
        |   ^~~~~~~~
        |   sane_start
  sm3600-scanutil.c:76:28: warning: passing argument 3 of ‘vfprintf’ makes pointer from integer without a cast [-Wint-conversion]
     76 |   vfprintf(stderr,szFormat,ap);
        |                            ^~
        |                            |
        |                            int
  In file included from ../include/sane/sanei_config.h:50,
                   from sm3600.c:70:
  .../host/x86_64-buildroot-linux-uclibc/sysroot/usr/include/stdio.h:339:23: note: expected ‘__va_list_tag *’ but argument is of type
 ‘int’
    339 |        __gnuc_va_list __arg);
        |        ~~~~~~~~~~~~~~~^~~~~
  In file included from sm3600.c:94:
  sm3600-scanutil.c:77:3: warning: implicit declaration of function ‘va_end’ [-Wimplicit-function-declaration]
     77 |   va_end(ap);
        |   ^~~~~~

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>