build: use dnl for comments in configure.ac
build: use dnl for comments in configure.ac

This simply means the comments are not copied into the executed
configure script.

jiangjianping/vo-amrwbenc,jiangjianping/vo-amrwbenc,mstorsjo/vo-amrwbenc,BelledonneCommunications/vo-amrwbenc,mstorsjo/vo-amrwbenc,BelledonneCommunications/vo-amrwbenc