RFR 8010280: jvm.cfg needs updating for non-server builds

[David Holmes]

Some background.

The jvm.cfg file, for which there is a per-architecture committed file 
in the repository, controls which VM's (client, server, minimal) are 
known, which is the default, whether there are other aliases and whether 
ergonomic selection is used.

Historically things were simple:
- 64-bit platforms had server only
- 32-bit platforms had client and server

then we acknowledged that some platforms may be client only and we added 
some support (originally in the old build then converted to the new 
build) for dynamically creating a jvm.cfg for the case of building 
client only.

Then the minimal VM was introduced and we potentially have three VMs to 
handle. To address this we initially added "-minimal KNOWN" to all the 
jvm.cfg files for platforms known to support the minimal VM - this was 
done under JDK-7198815 (and those changes are now reversed by this 
changeset.)

The problem after minimal was introduced was that the logic for 
"building client only" didn't account for building minimal (only or 
combined with client) and we need support for not-building-server. And 
that is what this changeset does.

This only affects 32-bit builds as there is no client nor minimal VM on 
64-bit. The basic operation is as follows:

- If building client+server then we use the committed jvm.cfg (which 
handles ergonomics if applicable), adding a "-minimal KNOWN" line if 
minimal is also selected;
- Otherwise we dynamically generate a jvm.cfg for the set of VMs being 
built, using these simple rules:
   - if client or server are present they are default
   - if client and/or server is absent then the absent VM is aliased to 
the default VM in that config
   - if minimal is not selected then it is absent from the jvm.cfg (we 
do not add any aliases for minimal**).

** The alias mechanism is useful for deprecating legacy VM names, and 
has also made testing more convenient. However I think it is a flawed 
mechanism for testing and our internal test infrastructure is moving 
away from arbitrarily using -client/-server when actually running 
server/client. If you ask for the minimal VM and it is not available I 
think you should get an error not silent use of a different VM. (Note: 
this selection doesn't affect SE Embedded as it defines jvm.cfg files 
using it's own rules/preferences.)

webrev:

http://cr.openjdk.java.net/~dholmes/8010280/webrev/

Thanks,
David