Fix Python test running under the JIT with ASAN

Summary:
The CinderX test runner redirects ASAN output to separate files
by calling the `__sanitizer_set_report_fd` function using ctypes
(https://fburl.com/code/rrbaqnt4). Under the hood, ctypes tries
to resolve `__sanitizer_set_report_fd` using `dlsym`. Resolving
`__sanitizer_set_report_fd` is currently failing (e.g. https://fburl.com/sandcastle/41sbdpx9)
because the symbol is defined but not exported from libpython. This causes
100% of tests to fail because the worker crashes before it can
even run the test. Export the symbol.

Reviewed By: alexmalyshev

Differential Revision: D61686959

fbshipit-source-id: 533e367e7e6491f168e0833f63b04ef811c83b5c

capi-functions

@@ -7,5 +7,7 @@
     _Ci*;
     /* Export strobe symbols needed for pyperf */
     __strobe_*;
+    /* CinderX's test runner uses this to redirect ASAN output */
+    __sanitizer_set_report_fd;
   };
 };