RFR: JDK-8039077: JPRT build configure not setting --with-update-version

[Erik Joelsson]

Please review this small fix for jdk8u.

When building jdk8u in JPRT, we still use the bridgebuild concept, where 
we let make translate a bunch of old build style environment variables 
to configure arguments. This patch adds one more such variable, which is 
needed in the update versions of jdk8: JDK_UPDATE_VERSION.

Bug: https://bugs.openjdk.java.net/browse/JDK-8039077
Patch inline:
diff -r b7750b6ee157 make/Jprt.gmk
--- a/make/Jprt.gmk
+++ b/make/Jprt.gmk
@@ -106,6 +106,9 @@
          ifdef ENABLE_SJAVAC
        @$(ECHO) " --enable-sjavac" >> $@.tmp
          endif
+        ifdef JDK_UPDATE_VERSION
+      @$(ECHO) " --with-update-version=$(JDK_UPDATE_VERSION)" >> $@.tmp
+        endif
          ifeq ($(HOTSPOT_AVAILABLE),false)
            ifdef ALT_JDK_IMPORT_PATH
          @$(ECHO) " --with-import-hotspot=$(call 
UnixPath,$(ALT_JDK_IMPORT_PATH)) " >> $@.tmp

/Erik