Add -ldl to libcommon link flags if it's needed for dlopen()

common/Makefile.am

@@ -52,4 +52,5 @@ libcommon_la_SOURCES = \
 libcommon_la_LIBADD = \
   -lcrypto \
   -lssl \
-  -lpthread
+  -lpthread \
+  $(DLOPEN_LIBS)

configure.ac

@@ -118,6 +118,12 @@ AC_ARG_ENABLE(pixman, AS_HELP_STRING([--enable-pixman],
               [], [enable_pixman=no])
 AM_CONDITIONAL(XRDP_PIXMAN, [test x$enable_pixman = xyes])
 
+# Check if -ldl is needed to use dlopen()
+DLOPEN_LIBS=
+AC_CHECK_FUNC(dlopen, [],
+              [AC_CHECK_LIB(dl, dlopen, [DLOPEN_LIBS=-ldl])])
+AC_SUBST(DLOPEN_LIBS)
+
 # checking for openssl
 AC_CHECK_HEADER([openssl/rc4.h], [],
   [AC_MSG_ERROR([please install libssl-dev or openssl-devel])],