merge revision(s) 40498:

	* thread_pthread.c (ruby_init_stack): Add STACK_GROW_DIR_DETECTION.
	  This fixes a compilation failure while cross-compiling for Tensilica
	  Xtensa Processor.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@40546 b2dd03c8-39d4-4d8f-98ff-823fe69b080e