package/libwebsockets: (re-)enable external poll loop support

Since version 3.2.0, libwebsockets does not compile its external loop
support code anymore. That code was put under LWS_WITH_EXTERNAL_POLL
compile option, which defaults to OFF.

Applications relying on that support need to turn that option on, so
let's add it to the package.

For example, when libwebsockets is enabled, mosquitto broker is built
with websocket support, but its code requires LWS_WITH_EXTERNAL_POLL
to be on, otherwise it gives compile-time warning hinting to unusable
websocket support:

https://github.com/eclipse/mosquitto/commit/1b24f625ea4ee77f3c4796ec2233d059f8c7977e

Signed-off-by: Luca Pesce <luca.pesce@vimar.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/libwebsockets/Config.in

@@ -9,5 +9,17 @@ config BR2_PACKAGE_LIBWEBSOCKETS
 
 	  https://libwebsockets.org/
 
+if BR2_PACKAGE_LIBWEBSOCKETS
+
+config BR2_PACKAGE_LIBWEBSOCKETS_EXT_POLL
+	bool "enable external poll loop support"
+	default y  # legacy, was previously always enabled
+	help
+	  Enable external poll loop support code. This was
+	  unconditionally compiled in for library versions
+	  prior to 3.2.0.
+
+endif
+
 comment "libwebsockets needs a toolchain w/ dynamic library"
 	depends on BR2_STATIC_LIBS

package/libwebsockets/libwebsockets.mk

@@ -94,4 +94,8 @@ ifeq ($(BR2_SHARED_LIBS),y)
 LIBWEBSOCKETS_CONF_OPTS += -DLWS_WITH_STATIC=OFF
 endif
 
+ifeq ($(BR2_PACKAGE_LIBWEBSOCKETS_EXT_POLL),y)
+LIBWEBSOCKETS_CONF_OPTS += -DLWS_WITH_EXTERNAL_POLL=ON
+endif
+
 $(eval $(cmake-package))