Shave a stack frame off asserts.

No-one cares about seeing "async_safe_fatal" (which you have to admit is a
pretty confusing name for an app developer anyway).

On arm:

     #00 pc 0001a43c  /system/lib/libc.so (abort+63)
     #1 pc 0001a627  /system/lib/libc.so (__assert+14)

And aarch64:

     #00 pc 000000000001d75c  /system/lib64/libc.so (abort+120)
     #1 pc 000000000001dad0  /system/lib64/libc.so (__assert+44)

Bug: N/A
Test: ran `crasher assert` and `crasher64 assert`
Change-Id: I00be71c566c74cdb00f8e95d634777155bc3da03

libc/async_safe/async_safe_log.cpp

@@ -567,10 +567,9 @@ void async_safe_fatal_va_list(const char* prefix, const char* format, va_list ar
   android_set_abort_message(msg);
 }
 
-void async_safe_fatal(const char* fmt, ...) {
+void async_safe_fatal_no_abort(const char* fmt, ...) {
   va_list args;
   va_start(args, fmt);
   async_safe_fatal_va_list(nullptr, fmt, args);
   va_end(args);
-  abort();
 }

libc/async_safe/include/async_safe/log.h

@@ -33,6 +33,7 @@
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <stdlib.h>
 
 // These functions do not allocate memory to send data to the log.
 
@@ -65,9 +66,19 @@ enum {
 };
 
 // Formats a message to the log (priority 'fatal'), then aborts.
-__noreturn void async_safe_fatal(const char* _Nonnull fmt, ...) __printflike(1, 2);
+// Implemented as a macro so that async_safe_fatal isn't on the stack when we crash:
+// we appear to go straight from the caller to abort, saving an uninteresting stack
+// frame.
+#define async_safe_fatal(...) \
+  do { \
+    async_safe_fatal_no_abort(__VA_ARGS__); \
+    abort(); \
+  } while (0) \
+
 
-// This function does return, so callers that want to abort, must do so themselves.
+// These functions do return, so callers that want to abort, must do so themselves,
+// or use the macro above.
+void async_safe_fatal_no_abort(const char* _Nonnull fmt, ...) __printflike(1, 2);
 #if defined(__arm__) || defined(__aarch64__) || defined(__x86_64__)
 void async_safe_fatal_va_list(
     const char* _Nullable prefix, const char* _Nonnull fmt, va_list);