Change the way libc++ is linked when use_custom_libcxx=1.

third_party/libc++/libc++.gyp

Index: third_party/libc++/libc++.gyp
diff --git a/third_party/libc++/libc++.gyp b/third_party/libc++/libc++.gyp
index b5f14f8471625d7841caae0fba9c1542e83f7f49..0e6fbe4ca9b364c9cfdb8aeab4eb22a8325f7843 100644
--- a/third_party/libc++/libc++.gyp
+++ b/third_party/libc++/libc++.gyp
@@ -5,14 +5,52 @@
 {
   'targets': [
     {
-      'target_name': 'libc++',
-      'type': 'shared_library',
+      'target_name': 'libcxx_proxy',
+      'type': 'none',
+      'dependencies=': [
+        'libc++',
+      ],
+      # Do not add dependency on libc++.so to dependents of this target. We
+      # don't want to pass libc++.so on the command line to the linker, as that
+      # would cause it to be linked into C executables which don't need it.
+      # Instead, we supply -stdlib=libc++ and let the clang driver decide.
+      'dependencies_traverse': 0,
       'variables': {
-        'prune_self_dependency': 1,
         # Don't add this target to the dependencies of targets with type=none.
         'link_dependency': 1,
       },
+      'direct_dependent_settings': {
+        'target_conditions': [
+          ['_type!="none"', {
+            'include_dirs': [
+              'trunk/include',
+              '../libc++abi/trunk/include',
+            ],
+            'cflags_cc': [
+              '-nostdinc++',
+            ],
+            'ldflags': [
+              '-stdlib=libc++',
+              # Normally the generator takes care of RPATH. Our case is special
+              # because the generator is unaware of the libc++.so dependency.
+              # Note that setting RPATH here is a potential security issue. See:
+              # https://code.google.com/p/gyp/issues/detail?id=315
+              '-Wl,-R,\$$ORIGIN/lib/',
+            ],
+            'library_dirs': [
+              '<(PRODUCT_DIR)/lib/',
+            ],
+          }],
+        ],
+      },
+    },
+    {
+      'target_name': 'libc++',
+      'type': 'shared_library',
       'dependencies=': [
+        # libc++abi is linked statically into libc++.so. This allows us to get
+        # both libc++ and libc++abi by passing '-stdlib=libc++'. If libc++abi
+        # was a separate DSO, we'd have to link against it explicitly.
         '../libc++abi/libc++abi.gyp:libc++abi',
       ],
       'sources': [
@@ -62,22 +100,6 @@
         '-Wstrict-overflow=4',
         '-nostdinc++',
       ],
-      'direct_dependent_settings': {
-        'target_conditions': [
-          ['_type!="none"', {
-            'include_dirs': [
-              'trunk/include',
-            ],
-            'cflags_cc': [
-              '-nostdinc++',
-            ],
-            'ldflags': [
-              '-stdlib=libc++',
-              '-L<(PRODUCT_DIR)/lib/',
-            ],
-          }],
-        ],
-      },
       'cflags_cc!': [
         '-fno-rtti',
       ],
@@ -87,7 +109,6 @@
       ],
       'ldflags': [
         '-nodefaultlibs',
-        '<(PRODUCT_DIR)/lib/libc++abi.so',
       ],
       'ldflags!': [
         # This somehow causes a warning from clang about an unused compilation