gdbinit: Use proper define syntax (GH-19557)

The-Compiler · web-flow · commit 122113528930 · 2020-04-23T05:49:26.000-07:00
Using `def` rather than `define` results in: Ambiguous command "def pu": define, define-prefix. Automerge-Triggered-By: @csabella
diff --git a/Misc/gdbinit b/Misc/gdbinit
@@ -160,7 +160,7 @@ document pystackv
   Print the entire Python call stack - verbose mode
 end
 
-def pu
+define pu
   set $uni = $arg0
   set $i = 0
   while (*$uni && $i++<100)
