Change "7901920: jh.jar is signed with a weak algorithm and its certificate is expired" introduced a logic to remove outdated signatures from jh.jar.

However, there's no default location for downloading jh.jar and probably most available versions (e.g. the one from Maven: http://central.maven.org/maven2/javax/help/javahelp/2.0.05/javahelp-2.0.05.jar) if not all of them don't contain signatures at all. This breaks the build because removing the signatures from the jar file with zip will fail:

zip warning: name not matched: META-INF/*.SF
zip warning: name not matched: META-INF/*.RSA
zip warning: name not matched: META-INF/*.DSA

zip error: Nothing to do! (/net/usr.work/openjdk/tools/jtreg/jtreg/build/images/jtreg/lib/jh.jar

The fix is trivial - just ignore the result of the zip step:

diff -r 1d23b6baaa4f make/jtreg.gmk
--- a/make/jtreg.gmk Thu Nov 30 18:28:29 2017 -0800
+++ b/make/jtreg.gmk Fri Dec 01 15:39:14 2017 +0100
@@ -249,7 +249,7 @@
  $(ECHO) JAVAHELP_HOME $(JAVAHELP_HOME)
  $(ECHO) JAVAHELP_JAR $(JAVAHELP_JAR)
  $(CP) $(JAVAHELP_JAR) $@
- $(ZIP) -d $@ 'META-INF/*.SF' 'META-INF/*.RSA' 'META-INF/*.DSA'
+ -$(ZIP) -d $@ 'META-INF/*.SF' 'META-INF/*.RSA' 'META-INF/*.DSA'
 
 ifdef JAVAHELP_JAR
     JTREG_IMAGE_JAVAHELP_JAR = $(JTREG_IMAGEDIR)/lib/jh.jar