Disable gcov instrumentation of functions using funclet-based exception handling

Summary: This patch fixes the crash from https://bugs.llvm.org/show_bug.cgi?id=34659 and https://bugs.llvm.org/show_bug.cgi?id=34833.

Reviewers: rnk, majnemer

Reviewed By: rnk, majnemer

Subscribers: majnemer, llvm-commits

Differential Revision: https://reviews.llvm.org/D38223

llvm-svn: 315677