Fix crash walking call stack on Linux.

tools/gyp/configurations_make.gypi

 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 {
   'variables': {
     'arm_cross_libc%': '/opt/codesourcery/arm-2009q1/arm-none-linux-gnueabi/libc',
     'dart_debug_optimization_level%': '2',
   },
   'target_defaults': {
@@ skipping 75 matching lines @@
             'cflags': [ '-O3', '-m32', '-msse2' ],
             'ldflags': [ '-m32' ],
         }]]
       },
 
       'Dart_Debug': {
         'cflags': [
           '-O<(dart_debug_optimization_level)',
           # The sampling profiler uses the frame pointer to walk the stack.
           '-fno-omit-frame-pointer',
+          # Clang on Linux will still omit frame pointers from leaf functions
+          # unless told otherwise:
+          # '-mno-omit-leaf-frame-pointer',
         ],
       },
 
       'Dart_Release': {
         'cflags': [
           '-O3',
           # The sampling profiler uses the frame pointer to walk the stack.
           '-fno-omit-frame-pointer',
+          # Clang on Linux will still omit frame pointers from leaf functions
+          # unless told otherwise:
+          # '-mno-omit-leaf-frame-pointer',
         ],
       },
     },
   },
 }