package/htop: fix uclibc build without wchar

Fix the following uclibc build failure without wchar raised since bump
to version 3.2.0 in commit b054353e59488713f841cd9ac9384b8a23f2e83a:

configure:5351: checking for /nvmedata/autobuild/instance-0/output-1/host/bin/i586-buildroot-linux-uclibc-gcc option to accept ISO C99
configure:5500: /nvmedata/autobuild/instance-0/output-1/host/bin/i586-buildroot-linux-uclibc-gcc  -c -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os -g1  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 conftest.c >&5
conftest.c:70:9: error: unknown type name 'wchar_t'
   70 |   const wchar_t *name;
      |         ^~~~~~~

[...]

configure: error: htop is written in C99. A newer compiler is required.

Fixes:
 - http://autobuild.buildroot.org/results/795bb4ae4f1a725c56353915c21fa784ca547c59

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/htop/htop.mk

@@ -13,6 +13,10 @@ HTOP_CONF_ENV = HTOP_NCURSES_CONFIG_SCRIPT=$(STAGING_DIR)/usr/bin/$(NCURSES_CONF
 HTOP_LICENSE = GPL-2.0+
 HTOP_LICENSE_FILES = COPYING
 
+# ac_cv_prog_cc_c99 is required for BR2_USE_WCHAR=n because the C99 test
+# provided by autoconf relies on wchar_t.
+HTOP_CONF_ENV += ac_cv_prog_cc_c99=-std=gnu99
+
 ifeq ($(BR2_PACKAGE_HWLOC),y)
 HTOP_CONF_OPTS += --enable-hwloc
 HTOP_DEPENDENCIES += hwloc