avoid using ifunc + ASan

avoid using ifunc + ASan

Summary:
Code that is using ifunc dies with SIGSEGV on startup when used
with ASan.

Here is gdb output: {P2882504}

Seems like `ifunc` dispatch is happening before ASan is initialized,
but ASan instrumentation logic being called from there.

Test Plan:
built affected unicorn binaries with ASan, ran them, verified
there is no more SIGSEGV

Reviewed By: meyering@fb.com

FB internal diff: D1013420