RFR(S): 8134889: Kitchensink stress test crashes with out of memory error

[Derek White]

Summary:
The remaining part of this bug deals with running out of address space 
on 32-bit JVMs running on Win64. This fix is simply to have a hard limit 
on GC threads (still larger than necessary) on 32-bit JVMs. The new 
limit is 16 (2 * switch_pt).

Note that this overlaps somewhat with several "# of GC thread" bugs 
including:
  - 8131932 <https://bugs.openjdk.java.net/browse/JDK-8131932> : 
Ergonomics oversize number of GC threads for small JVMs on large systems
  - 8153225 <https://bugs.openjdk.java.net/browse/JDK-8153225>: G1 
creates too many concurrent refinement threads by default
  - 7189147 <https://bugs.openjdk.java.net/browse/JDK-7189147>: GC 
threads should be created as needed not all at once

Doing the correct thing in general will require a lot more performance 
analysis. The fix here is simple, only affects 32-bit JVMs running on >= 
24 core machines, and will reduce OOM crashes in nightly testing.

BUG: 8134889 <https://bugs.openjdk.java.net/browse/JDK-8134889>
WEBREV: http://cr.openjdk.java.net/~drwhite/8134889/webrev.01/
TESTS: jprt

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