[lld/mac] add a comment pointing to a test that took me a while to find

Author: nico

lld/test/MachO/private-extern.s

@@ -20,6 +20,9 @@
 # EXPORTS-NM-DAG: (__TEXT,__cstring) non-external (was a private external) _foo
 # EXPORTS-NM-DAG: (__TEXT,__cstring) external _bar
 
+# Tests that weak private_exten symbols aren't referenced in the
+# weak bind table are in weak-private.extern.s
+
 #--- basics.s
 .section __TEXT,__cstring
 

lld/test/MachO/weak-private-extern.s

@@ -2,6 +2,7 @@
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos %s -o %t.o
 # RUN: %lld -dylib %t.o -o %t.dylib -lSystem
+
 # RUN: llvm-objdump --macho --weak-bind %t.dylib | FileCheck %s
 # CHECK-NOT: __got
 # CHECK-NOT: __la_symbol_ptr