Tighten handling of pthread_create errors on Linux.

Tighten handling of pthread_create errors on Linux.

The return value of pthread_create is now checked to be 0.
Tests on MIPS boards had some silent and hard to find timeouts and errors related to this.
This ensures a proper error message and shutdown if a thread could not be started.

BUG=
TEST=

Review URL: http://codereview.chromium.org/8497041
Patch from Gergely Kis <gergely@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9945 ce2b1a6d-e550-0410-aec6-3dcde31c8c00