mac: In component builds, link against libc++.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 944dcb6eebb257bf06dda0140bcd09e45face065..62f322753b9a1527d30c23c95c81b3a07d81f7a8 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -5286,6 +5286,29 @@
             # specified or not.
             '-fno-strict-aliasing',  # See http://crbug.com/32204.
           ],
+          'conditions': [
+            ['component=="shared_library"', {
+              # In component builds, link to the system libc++. This requires
+              # OS X 10.7, but we currently pass -mmacosx-version-min=10.6.
+              # Xcode's clang complains about this, but our open-source bundled
+              # chromium clang doesn't -- it just doesn't implicitly add -lc++
+              # either.  Explicitly add that flag.  This has the effect of
+              # making everything depend on libc++, which means component-build
+              # binaries won't run on 10.6 (no libc++ there), but for a
+              # developer-only configuration that's ok.
+              # (We don't want to raise the deployment target yet so that
+              # official and dev builds have the same deployment target.  This
+              # affects things like which functions are considered deprecated.)
+              'CLANG_CXX_LIBRARY': 'libc++',  # -stdlib=libc++
+              'target_conditions': [
+                ['_type!="static_library"', {
+                  # OTHER_LDFLAGS is passed to both .so and .a links, but only
+                  # the former type understands it.  Hence the _type check.
+                  'OTHER_LDFLAGS': [ '-lc++' ],

[Mark Mentovai, 2015/10/16 22:34:59]

I thought CLANG_CXX_LIBRARY would have been enough. Is it not? What does the
link line look like now? I don’t want to wind up with something like -lc++
-lstdc++.

[Nico, 2015/10/16 23:08:35]

Excellent question! I thought it wasn't enough because we pass
-mmin-macosx-version=10.6, but it turns out I screwed up my local testing and
this isn't needed. Done.

+                }],
+              ]
+            }],
+          ],
         },
         'target_conditions': [
           ['_type=="executable"', {