Windows SRWLOCK requires you call different functions here. Split
them up in preparation for switching Windows from CRITICAL_SECTION.

BUG=37

Change-Id: I7b5c6a98eab9ae5bb0734b805cfa1ff334918f35
Reviewed-on: https://boringssl-review.googlesource.com/8080
Reviewed-by: Adam Langley <agl@google.com>

Trusty doesn't have setjmp.h and nor does it have threads.

Change-Id: I005f7a009a13e6632513be9fab2bbe62294519a4
Reviewed-on: https://boringssl-review.googlesource.com/4660
Reviewed-by: Adam Langley <agl@google.com>