Add '-ldl' to Linux targets that use dynamic loader functions.

gpu/gpu.gyp

 # Copyright (c) 2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'chromium_code': 1,
     # This is defined here because we need to compile this set of files
     # twice with different defines. Once so it calls real GL, again so it
     # calls mock GL for the unit tests.
@@ skipping 44 matching lines @@
           {
             'all_dependent_settings': {
               'defines': [
                 'GL_GLEXT_PROTOTYPES',
               ],
               'ldflags': [
                 '-L<(PRODUCT_DIR)',
               ],
               'libraries': [
                 '-lX11',
+                # For dlsym() in '../third_party/glew/src/glew.c'
+                '-ldl',
               ],
             },
           },
         ],
         [ 'OS=="mac"',
           {
             'direct_dependent_settings': {
               'libraries': [
                 '$(SDKROOT)/System/Library/Frameworks/OpenGL.framework',
               ],
@@ skipping 363 matching lines @@
       },
     ],
   ],
 }
 
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