scripts: ext-toolchain: add support for musl

Openwrt now supports only glibc and musl. Add support for musl and
rework the libc check to handle the new config flags and correctly
compile package basend on that.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

scripts/ext-toolchain.sh

@@ -369,8 +369,18 @@ print_config() {
 	echo "CONFIG_TOOLCHAIN_PREFIX=\"$prefix\"" >> "$config"
 	echo "CONFIG_TARGET_NAME=\"$target\"" >> "$config"
 
-	if [ "$LIBC_TYPE" != glibc ]; then
-		echo "CONFIG_TOOLCHAIN_LIBC=\"$LIBC_TYPE\"" >> "$config"
+	if [ -f "$config" ]; then
+		sed -i '/CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_MUSL/d' "$config"
+		sed -i '/CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_GLIBC/d' "$config"
+	fi
+
+	if [ "$LIBC_TYPE" == glibc ]; then
+		echo "CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_GLIBC=y" >> "$config"
+	elif [ "$LIBC_TYPE" == musl ]; then
+		echo "CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_MUSL=y" >> "$config"
+	else
+		echo "Can't detect LIBC type. Aborting!" >&2
+		return 1
 	fi
 
 	local lib