introduce nimMaxHeap define to fight memory overcommit

tools/nimsuggest/nimsuggest.nim.cfg

@@ -8,6 +8,12 @@ path:"$lib/packages/docutils"
 
 define:useStdoutAsStdmsg
 define:nimsuggest
+# die when nimsuggest uses more than 4GB:
+@if cpu32:
+  define:"nimMaxHeap=2000"
+@else:
+  define:"nimMaxHeap=4000"
+@end
 
 #cs:partial
 #define:useNodeIds