[RFC] Per-directory libjava builds

[Paolo Bonzini]

>>>This patch builds libjava one directory at a time rather than one file
>>>at a time.  It improves build times by 20-30% on average; 
>>>      
>>>
>What about memory peak usage during build?
>  
>
I have not measured it, but I have successfully built libjava with a 128 
MB ulimit.

atelier:~ bonzinip$ ulimit -d -m -v -H
data seg size         (kbytes, -d) 131072
max memory size       (kbytes, -m) 131072
virtual memory        (kbytes, -v) 131072

Also, the biggest .o that I build is javax.swing (3 MB).  Even without 
my patch, some .o files are built that include multiple classes: one of 
them, gnu-xml.o, is bigger than this (3.7 MB).

Paolo