[libc++] Always define a key function for std::bad_function_call in the dylib

However, whether applications rely on the std::bad_function_call vtable
being in the dylib is still controlled by the ABI macro, since changing
that would be an ABI break.

Also separate preprocessor definitions for whether to use a key function
and whether to use a `bad_function_call`-specific `what` message
(`what` message is mandated by [LWG2233](http://wg21.link/LWG2233)).

Differential Revision: https://reviews.llvm.org/D92397

libcxx/test/std/utilities/function.objects/bind/func.bind/func.bind.bind/copy.pass.cpp

@@ -6,7 +6,18 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
+// Address Sanitizer doesn't instrument weak symbols on Linux. When a key
+// function is defined for bad_function_call's vtable, its typeinfo and vtable
+// will be defined as strong symbols in the library and weak symbols in other
+// translation units. Only the strong symbol will be instrumented, increasing
+// its size (due to the redzone) and leading to a serious ODR violation
+// resulting in a crash.
+// Some relevant bugs:
+// https://github.com/google/sanitizers/issues/1017
+// https://github.com/google/sanitizers/issues/619
+// https://github.com/google/sanitizers/issues/398
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68016
+// UNSUPPORTED: c++03, asan
 // XFAIL: LIBCXX-AIX-FIXME
 
 // <functional>