restored backtrace on failure

for Linux and Mac OS-X.

Note : the backtraces fires up through a trap
before the sanitizer get a chance to report.
There are situations where the sanitizer report is actually preferable.

It might be good to consider a kind of build macro
which can disable backtrace
when sanitizer is enabled.

programs/zstdcli.c

@@ -547,7 +547,7 @@ int main(int argCount, const char* argv[])
     memset(&compressionParams, 0, sizeof(compressionParams));
 
     /* init crash handler */
-    //FIO_addAbortHandler();
+    FIO_addAbortHandler();
 
     /* command switches */
     for (argNb=1; argNb<argCount; argNb++) {