qdecoder: autoreconf and fix c99 detection

Fixes http://autobuild.buildroot.net/results/da8/da8ce760cdabeb9d4cda00dcc801817e4b4eb12c/

As we're patching configure.ac we need to autoreconf the package.
After reconf, the c99 check fails, so force it like we do elsewhere.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/qdecoder/qdecoder.mk

@@ -8,6 +8,9 @@ QDECODER_VERSION = r12.0.5
 QDECODER_SITE = $(call github,wolkykim,qdecoder,$(QDECODER_VERSION))
 QDECODER_LICENSE = BSD-2
 QDECODER_LICENSE_FILES = COPYING
+# we patch configure.ac
+QDECODER_AUTORECONF = YES
+QDECODER_CONF_ENV = ac_cv_prog_cc_c99='-std=gnu99'
 
 QDECODER_INSTALL_STAGING = YES