[tsan] Annotate function parameters with attribute 'noescape'.

This commit annotates the block parameters of the following functions
declared in compiler-rt with 'noescape':

- dispatch_sync
- dispatch_barrier_sync
- dispatch_once
- dispatch_apply

This is needed to commit the patch that adds support for 'noescape' in
clang (see https://reviews.llvm.org/D32210) since these functions are
annotated with 'noescape' in the SDK header files.

Differential Revision: https://reviews.llvm.org/D32210

llvm-svn: 313929