common: merge only_for_archs and noarch=yes into one.

* noarch=yes is replaced with archs=noarch
* only_for_archs= is renamed to archs=
* archs= allows the use of wildcards and negations; first matching rule applies:
  * archs="*-musl" will build the pkg only for musl-libcs
  * archs="~*-musl" will build the pkg only on non-musl-libc
  * archs="x86_64-musl ~*-musl" will build for x86_64-musl and any non-musl
    arch.
* archs= defaults to "*"

common/hooks/do-pkg/00-gen-pkg.sh

@@ -97,14 +97,14 @@ hook() {
 	local arch= binpkg= repo= _pkgver= _desc= _pkgn= _pkgv= _provides= \
 		_replaces= _reverts= f= found_dbg_subpkg=
 
-	if [ -n "$noarch" ]; then
+	if [ "${archs// /}" = "noarch" ]; then
 		arch=noarch
 	elif [ -n "$XBPS_TARGET_MACHINE" ]; then
 		arch=$XBPS_TARGET_MACHINE
 	else
 		arch=$XBPS_MACHINE
 	fi
-	if [ -z "$noarch" -a -z "$XBPS_CROSS_BUILD" -a -n "$XBPS_ARCH" -a "$XBPS_ARCH" != "$XBPS_TARGET_MACHINE" ]; then
+	if [ "${archs// /}" != "noarch" -a -z "$XBPS_CROSS_BUILD" -a -n "$XBPS_ARCH" -a "$XBPS_ARCH" != "$XBPS_TARGET_MACHINE" ]; then
 		arch=${XBPS_ARCH}
 	fi