[ASAN] Add macro denoting availability of new `__asan_handle_no_return()` function.

Summary:
Libc++abi attempts to use the newly added `__asan_handle_no_return()` when built under ASAN. Unfortunately older versions of compiler-rt do not provide this symbol, and so libc++abi needs a way to detect if `asan_interface.h` actually provides the function.

This patch adds the macro `SANITIZER_ASAN_INTERFACE_HAS_HANDLE_NO_RETURN` which can be used to detect the availability of the new function.

Reviewers: phosek, kcc, vitalybuka, alekseyshl

Reviewed By: phosek

Subscribers: mclow.lists, cfe-commits

Differential Revision: https://reviews.llvm.org/D37871

llvm-svn: 313303

compiler-rt/include/sanitizer/asan_interface.h

@@ -148,6 +148,10 @@ extern "C" {
   // before things like _exit and execl to avoid false positives on stack.
   void __asan_handle_no_return(void);
 
+  // Required to allow ASAN versions of libc++abi to build against older
+  // versions of compiler-rt that do not provide this interface.
+# define SANITIZER_ASAN_INTERFACE_HAS_HANDLE_NO_RETURN
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif