The build of jdk11u-dev may fail(reproduced on the latest cygwin and msys2) with the following error:

/usr/bin/cp: cannot stat '/jdk.crypto.ec/*': No such file or directory
make[3]: *** [CompileJavaModules.gmk:646: /openjdk/jdk11u-dev-msys/build/windows-x86_64-normal-server-release/jdk/modules/jdk.crypto.ec/_imported.marker] Error 1
make[2]: *** [make/Main.gmk:199: jdk.crypto.ec-java] Error 2
make[2]: *** Waiting for unfinished jobs....

The root cause lies in CompileJavaModules.gmk. The following block is executed even when the source directory $(IMPORT_MODULES_CLASSES)/$(MODULE) does not exist:

ifneq ($(wildcard $(IMPORT_MODULES_CLASSES)/$(MODULE)), )
  $(JDK_OUTPUTDIR)/modules/$(MODULE)/_imported.marker: \
      $(call FindFiles, $(IMPORT_MODULES_CLASSES)/$(MODULE))
$(call MakeDir, $(@D))
        # Do not delete marker and build meta data files
$(RM) -r $(filter-out $(@D)/_%, $(wildcard $(@D)/*))
$(CP) -R $(IMPORT_MODULES_CLASSES)/$(MODULE)/* $(@D)/
$(TOUCH) $

This issue was resolved in jdk17u+ by JDK-8220383, which simplified the import logic and added proper checks to avoid such failures.