testing/htmlcxx: fix build on loongarch64

Update config sub for loongarch64.

testing/htmlcxx/APKBUILD

@@ -11,6 +11,11 @@ options="!check" # no testsuite
 subpackages="$pkgname-dev"
 source="$pkgname-$pkgver.tar.gz::https://sourceforge.net/projects/htmlcxx/files/v$pkgver/htmlcxx-$pkgver.tar.gz"
 
+prepare() {
+	default_prepare
+	update_config_sub
+}
+
 build() {
 	# gcc12 defaults to 17 which fails due to throw()
 	export CXXFLAGS="$CXXFLAGS -std=c++14"