test: fix test under ASAN and MSAN

When we're running tests under ASAN or MSAN, they're compiled with -O1, which
enables tail call elimination. This causes backtrace_test to fail: the compiler
performs tail call elimination for call3_nothrow, but it can't for call3_throw,
leading to a mismatched frame count. Disable tail call elimination (and
inlining, just to be explicit) to avoid this.

Patch by Shoaib Meenai!

llvm-svn: 279935