RFR: Fix jtreg test runtime/StackGuardPages/

[Siebenborn, Axel]

Hi,

the test  runtime/StackGuardPages/ fails, as AttachCurrentThread() returns with an error. The reason is a stackoverflow while trying to run java Thread.init().
The default pthread stack size is 80 K, much less than on other Unixes. 

The first fix is to check the pthread default stacksize and increase it if it's less than 160K.

Webrev a:
http://cr.openjdk.java.net/~asiebenborn/jtreg_StackGuardPages/webrev_a/ 

However, the reason we need that much stack, just to run a single java method, is the large amount of shadow pages.
The second fix is just to add a flag to JNI_CreateJavaVM, to set the number of shadow pages to a lower value. However, a change in globals_x86.hpp is needed to allow smaller minimum for that value. Here I miss a macro like MUSL_OLNLY(code).

Webrev b:
http://cr.openjdk.java.net/~asiebenborn/jtreg_StackGuardPages/webrev_b/

I'm unsure which change to use.
What do you think?

Regards,
Axel