configure.ac: use AC_CONFIG_HEADERS
configure.ac: use AC_CONFIG_HEADERS

Use documented AC_CONFIG_HEADERS instead of AC_CONFIG_HEADER alias
that might be removed in future automake versions.

Related to tracker item 3600293, and to the previous commit.

davel/sox,davel/sox,davel/sox,cbagwell/sox,cbagwell/sox,Distrotech/sox,pcqpcq/sox,davel/sox,cbagwell/sox,Distrotech/sox,pcqpcq/sox,uklauer/sox,Distrotech/sox,Distrotech/sox,CaptainHayashi/sox,cbagwell/sox,CaptainHayashi/sox,pcqpcq/sox,uklauer/sox,uklauer/sox,CaptainHayashi/sox,pcqpcq/sox,uklauer/sox,CaptainHayashi/sox