mklib: Teach mklib to fail build if link fails on cygwin

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Signed-off-by: Brian Paul <brianp@vmware.com>

(cherry picked from commit 551c96979e643b409535afe868c42cac0d2285ad)

bin/mklib

@@ -977,6 +977,11 @@ case $ARCH in
 
             # make lib
             ${LINK} ${OPTS} ${LDFLAGS} -o ${CYGNAME}-${MAJOR}.dll ${OBJECTS} ${DEPS}
+            # make build fail if link failed
+            es=$?
+            if [ "$es" -ne "0" ]; then
+                exit $es
+            fi
             # make usual symlinks
             ln -s ${LIBNAME}-${MAJOR}.dll.a ${LIBNAME}.dll.a
             # finish up