Raise MAX_VM_MEMORY

[Henri Gomez]

For some days, I got OOM in Javadoc stages for jdk8 and lambda on Linux

I think others build OpenJDK 8 on 32bits systems could be in same
trouble and I suggest to raise it from 612m to 768m.


--- jdk/make/docs/Makefile.orig	2012-09-16 14:38:19.714697484 +0200
+++ jdk/make/docs/Makefile	2012-09-16 14:38:26.767697710 +0200
@@ -73,7 +73,7 @@
 else ifeq ($(ARCH),universal)
   MAX_VM_MEMORY = 1024
 else
-  MAX_VM_MEMORY = 612
+  MAX_VM_MEMORY = 768
 endif

 # List of all possible directories for javadoc to look for sources