[ASan] Skip dump_instruction_bytes test on non-x86 targets

Summary: This test case is blatantly x86-specific, so skip it on other targets.

Reviewers: kcc, eugenis, earthdok, samsonov

Reviewed By: samsonov

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D6216

llvm-svn: 221778