Fix Die() after pthread_exit call on macOS

Summary:
Scoped interceptor should not be used when calling real pthread_exit().
On macOS C++ destructors are not called by pthread_exit(), and later check for empty thread ignore set fails.

Patch by Yuri Per.

Reviewers: dvyukov, vitalybuka

Reviewed By: vitalybuka

Subscribers: vitalybuka, thegameg, kubamracek, jfb, llvm-commits, #sanitizers

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D57963

llvm-svn: 353561