```
$ make CONF=server-release bootcycle-images
Building target 'bootcycle-images' in configuration 'macosx-x86_64-server-release'
Boot cycle build step 2: Building a new JDK image using previously built image
Building target 'product-images' in configuration 'macosx-x86_64-server-release'
[bootcycle] Compiling 8 files for BUILD_TOOLS_LANGTOOLS
warning: [options] system modules path not set in conjunction with -source 14
error: warnings found and -Werror specified
1 error
1 warning
```

It might be fixed by
```
diff -r 8b5600a42034 make/Main.gmk
--- a/make/Main.gmk Wed Apr 29 10:05:30 2020 +0200
+++ b/make/Main.gmk Wed Apr 29 18:35:53 2020 +0800
@@ -353,7 +353,8 @@
          $(call LogWarn, Boot cycle build step 2: Building a new JDK image using previously built image)
          $(call MakeDir, $(OUTPUTDIR)/bootcycle-build)
          +$(MAKE) $(MAKE_ARGS) -f $(TOPDIR)/make/Init.gmk PARALLEL_TARGETS=$(BOOTCYCLE_TARGET) \
- LOG_PREFIX="[bootcycle] " JOBS= SPEC=$(dir $(SPEC))bootcycle-spec.gmk main
+ LOG_PREFIX="[bootcycle] " JOBS= SPEC=$(dir $(SPEC))bootcycle-spec.gmk \
+ JAVA_WARNINGS_ARE_ERRORS="" main
         else
          $(call LogWarn, Boot cycle build disabled when cross compiling)
         endif
```