package/ipmiutil: fix uclibc build without wchar

For an unknown reason, wchar_t is incorrectly detected with uclibc
resulting in the following build failure:

In file included from igetevent.c:136:
imb_api.h:150:5: error: unknown type name 'wchar_t'
  150 |     wchar_t *Buffer;
      |     ^~~~~~~

The build failure can be reproduced even when reverting bump to version
3.1.8.

Fixes:
 - http://autobuild.buildroot.org/results/e9ff3bd08e106dc834968bf5e4296ce8299027f8

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 7b4937a1709a88f90abbeac48e2e2db33b83d44b)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/ipmiutil/ipmiutil.mk

@@ -10,6 +10,7 @@ IPMIUTIL_LICENSE = BSD-3-Clause
 IPMIUTIL_LICENSE_FILES = COPYING
 
 IPMIUTIL_MAKE = $(MAKE1)
+IPMIUTIL_CONF_ENV = ac_cv_type_wchar_t=$(if $(BR2_USE_WCHAR),yes,no)
 
 # aclocal.m4 is newer than config.h.in. Touch the latter to avoid autoreconf
 define IPMIUTIL_TOUCH_CONFIG_H_IN