[urgent] RFR: JDK-8141574: recent change for 8141543 breaks all builds

[Erik Joelsson]

Hello,

Please review this fix for the current build break in jdk9-dev. It seems 
initializing variables to the empty string in shell requires quotes.

Bug: https://bugs.openjdk.java.net/browse/JDK-8141574
Patch:
diff -r 4ba17e992008 common/autoconf/flags.m4
--- a/common/autoconf/flags.m4
+++ b/common/autoconf/flags.m4
@@ -945,9 +945,9 @@

   if test "x$WARNINGS_AS_ERRORS" = "xfalse"; then
     # Set legacy hotspot variable
-    HOTSPOT_SET_WARNINGS_AS_ERRORS=WARNINGS_ARE_ERRORS=
+    HOTSPOT_SET_WARNINGS_AS_ERRORS="WARNINGS_ARE_ERRORS="
   else
-    HOTSPOT_SET_WARNINGS_AS_ERRORS=
+    HOTSPOT_SET_WARNINGS_AS_ERRORS=""
   fi

   AC_SUBST(WARNINGS_AS_ERRORS)

/Erik