abuild: clear inherit provides and install_if for subpackages

Unexpected result will happen if subpackages inherits the provides or
install_if from main package. So we clear them.

abuild.in

@@ -947,6 +947,11 @@ archcheck() {
 
 prepare_package() {
 	msg "Preparing ${subpkgname:+sub}package ${subpkgname:-$pkgname}..."
+	if [ -n "$subpkgname" ]; then
+		# the subpackages should not inherit those
+		provides=""
+		install_if=""
+	fi
 	stripbin
 	prepare_metafiles \
 		&& prepare_trace_rpaths \