cdp: Makefile - use pkg-config if xml2-config is not found

- GH #2199

(cherry picked from commit 2749962b8354be1731ab68a0ae4aa0fac4f944e1)

src/modules/cdp/Makefile

@@ -6,6 +6,12 @@ NAME=cdp.so
 
 ifeq ($(CROSS_COMPILE),)
 XML2CFG=$(shell which xml2-config)
+ifeq ($(XML2CFG),)
+XML2CFG=$(shell \
+	if pkg-config --exists libxml-2.0; then \
+		echo 'pkg-config libxml-2.0'; \
+	fi)
+endif
 endif
 
 ifneq ($(XML2CFG),)