7012642: G1: JumbleGC002 test aborts with segmentation violation due to uncaught stack overflow

Summary: With recent G1 allocation path changes, the value of StackShadowPages in fast debug builds of the JVM, is no longer large enough to prevent the JVM C++ code from touching the stack guard pages. Increase the value of StackShadowPages to a suitable value.
Reviewed-by: ysr, tonyp, coleenp

src/cpu/x86/vm/globals_x86.hpp

@@ -62,7 +62,7 @@ define_pd_global(intx, StackRedPages, 1);
 // due to lack of optimization caused by C++ compiler bugs
 define_pd_global(intx, StackShadowPages, SOLARIS_ONLY(20) NOT_SOLARIS(6) DEBUG_ONLY(+2));
 #else
-define_pd_global(intx, StackShadowPages, 3 DEBUG_ONLY(+1));
+define_pd_global(intx, StackShadowPages, 3 DEBUG_ONLY(+5));
 #endif // AMD64
 
 define_pd_global(intx, PreInflateSpin,           10);