--- a/make/common/SetupJavaCompilers.gmk	Thu Feb 01 09:16:03 2018 -0800
+++ b/make/common/SetupJavaCompilers.gmk	Thu Feb 01 09:20:40 2018 -0800
@@ -26,13 +26,16 @@
 ifndef _SETUP_GMK
 _SETUP_GMK := 1
 
+# Include custom extension hook
+$(eval $(call IncludeCustomExtension, common/SetupJavaCompilers.gmk))
+
 include JavaCompilation.gmk
 
-DISABLE_WARNINGS := -Xlint:all,-deprecation,-removal,-unchecked,-rawtypes,-cast,-serial,-dep-ann,-static,-fallthrough,-try,-varargs,-empty,-finally
+DISABLE_WARNINGS ?= -Xlint:all,-deprecation,-removal,-unchecked,-rawtypes,-cast,-serial,-dep-ann,-static,-fallthrough,-try,-varargs,-empty,-finally
 
 # If warnings needs to be non-fatal for testing purposes use a command like:
 # make JAVAC_WARNINGS="-Xlint:all -Xmaxwarns 10000"
-JAVAC_WARNINGS := -Xlint:all -Werror
+JAVAC_WARNINGS ?= -Xlint:all -Werror
 
 # The BOOT_JAVAC setup uses the boot jdk compiler to compile the tools
 # and the interim javac, to be run by the boot jdk.