review request for 7142641: -Xshared:on fails on ARM

[Dean Long]

http://cr.openjdk.java.net/~dlong/7142641/webrev.0/
Summary of changes:    3 lines changed: 0 ins; 2 del; 1 mod; 5538 unchg

The Class Data Sharing file is mapped "shared" on linux, which places 
extra constraints on which virtual address a file offset can use.  This 
is to ensure consistency on certain platforms with aliasing caches.  
However as the CDS file is opened read-only, mapping it "shared" has no 
benefit and can cause the mmap to fail.  The simplest fix is to change 
the mapping to "private".

Tested on linux arm platform with aliasing cache.  Installed CDS with 
-Xshare:dump then ran through some vm tests as a sanity check.

This bug is on the 7u4 watch list.

dl