Add compile time checks for whether -lanl is required

Prior to glibc 2.34 this was required

CMakeLists.txt

@@ -23,6 +23,8 @@ if(APPLE)
 endif(APPLE)
 
 include(GNUInstallDirs)
+include(CMakePushCheckState)
+include(CheckSourceCompiles)
 
 option(WITH_BUNDLED_DEPS "Build with bundled dependencies?" ON)
 option(WITH_TLS

config.mk

@@ -318,7 +318,10 @@ ifeq ($(WITH_EC),yes)
 endif
 
 ifeq ($(WITH_ADNS),yes)
-	BROKER_LDADD:=$(BROKER_LDADD) -lanl
+	NEED_LIBANL:=$(shell printf 'int main(){return 0;}' | gcc -D_GNU_SOURCE -lanl -o /dev/null -x c - 2>/dev/null || echo yes)
+	ifeq ($(NEED_LIBANL),yes)
+		BROKER_LDADD+=-lanl
+	endif
 	BROKER_CPPFLAGS:=$(BROKER_CPPFLAGS) -DWITH_ADNS
 endif
 

src/CMakeLists.txt

@@ -165,12 +165,31 @@ endif (WITH_DLT)
 
 set (MOSQ_LIBS ${MOSQ_LIBS} OpenSSL::SSL)
 # Check for getaddrinfo_a
-include(CheckLibraryExists)
-check_library_exists(anl getaddrinfo_a  "" HAVE_GETADDRINFO_A)
-if (HAVE_GETADDRINFO_A AND WITH_ADNS)
-	add_definitions("-DWITH_ADNS")
-	add_definitions(-DHAVE_GETADDRINFO_A)
-	set (MOSQ_LIBS ${MOSQ_LIBS} anl)
+# Prior to glibc 2.34 this required linking with anl
+if(WITH_ADNS)
+	cmake_push_check_state()
+	set(ANL_CODE "
+		#include <stdlib.h>
+		#include <netdb.h>
+		int main(){
+			return getaddrinfo_a(0, NULL, 0, NULL);
+		}
+	")
+	check_source_compiles(C "${ANL_CODE}" HAVE_GETADDRINFO_A)
+	if(HAVE_GETADDRINFO_A)
+		add_definitions(mosquitto PRIVATE "WITH_ADNS")
+	else()
+		set(CMAKE_REQUIRED_LIBRARIES "anl")
+		check_source_compiles(C "${ANL_CODE}" HAVE_GETADDRINFO_A_LIBANL)
+
+		if(HAVE_GETADDRINFO_A_LIBANL)
+			add_definitions(mosquitto PRIVATE "WITH_ADNS")
+			set (MOSQ_LIBS ${MOSQ_LIBS} anl)
+		else()
+			message(FATAL_ERROR "WITH_ADNS is set, but getaddrinfo_a() is not available.")
+		endif()
+	endif()
+	cmake_pop_check_state()
 endif (HAVE_GETADDRINFO_A AND WITH_ADNS)