osmesa: Link with -ldl for dlopen code

Now that the dlopen wrappers are built into libmesa.a, we need to link
standalone libOSMesa with libdl to resolve dlopen and friends on
platforms that need it.
(cherry picked from commit 4795dd5950)

configure.ac

@@ -826,12 +826,12 @@ case "$mesa_driver" in
 osmesa)
     # only link libraries with osmesa if shared
     if test "$enable_static" = no; then
-        OSMESA_LIB_DEPS="-lm -lpthread $SELINUX_LIBS"
+        OSMESA_LIB_DEPS="-lm -lpthread $SELINUX_LIBS $DLOPEN_LIBS"
     else
         OSMESA_LIB_DEPS=""
     fi
     OSMESA_MESA_DEPS=""
-    OSMESA_PC_LIB_PRIV="-lm -lpthread $SELINUX_LIBS"
+    OSMESA_PC_LIB_PRIV="-lm -lpthread $SELINUX_LIBS $DLOPEN_LIBS"
     ;;
 *)
     # Link OSMesa to libGL otherwise
@@ -845,9 +845,6 @@ osmesa)
     OSMESA_PC_REQ="gl"
     ;;
 esac
-if test "$enable_static" = no; then
-    OSMESA_LIB_DEPS="$OSMESA_LIB_DEPS"
-fi
 OSMESA_PC_LIB_PRIV="$OSMESA_PC_LIB_PRIV"
 AC_SUBST([OSMESA_LIB_DEPS])
 AC_SUBST([OSMESA_MESA_DEPS])