GN: Get Mac build working for IPC target at least.

build/config/sysroot.gni

Index: build/config/sysroot.gni
diff --git a/build/config/linux/sysroot.gni b/build/config/sysroot.gni
similarity index 60%
rename from build/config/linux/sysroot.gni
rename to build/config/sysroot.gni
index 4d14915ecdebb6d8c3c7856199b9ea28647cffe0..a448550679f6e35fc20d08f37bfc47efce80e927 100644
--- a/build/config/linux/sysroot.gni
+++ b/build/config/sysroot.gni
@@ -19,9 +19,23 @@ if (is_linux && is_chrome_branded && is_official_build && !is_chromeos) {
     sysroot = ""
   }
 } else if (is_mac) {
+  declare_args() {

[brettw, 2014/01/08 00:24:20]

I think this should go in a separate mac SDK .gni file that this one imports.
The reason is that the SDK location doesn't really have anything to do with the
sysroot. If another BUILD.gn file wants the Mac SDK location, it makes more
sense for them to import the SDK .gni file thatn the sysroot one.

You can see my equivalent Windows one:
https://codereview.chromium.org/126073005/

So maybe call it build/config/mac/mac_sdk.gni (or something), move this code
there, and replace it with an import.

[bbudge, 2014/01/08 01:13:15]

Done.

+    # Minimum supported version of the Mac SDK.
+    mac_sdk_min = "10.6"
+
+    # Path to the Mac SDKs, not including a backslash at the end.
+    mac_sdk_path = "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs"
+  }
+
   # Set which SDK to use.
-  # TODO(brettw) this needs to be configurable somehow.
-  sysroot = "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk"
+  if (is_chrome_branded && is_official_build) {
+    find_sdk_args = ["--verify", mac_sdk_min "--sdk_path=" + mac_sdk_path]
+  } else {
+    find_sdk_args = [mac_sdk_min]
+  }
+  mac_sdk_version =
+      exec_script("//build/mac/find_sdk.py", find_sdk_args, "list lines")
+  sysroot = mac_sdk_path + "/MacOSX" + mac_sdk_version[0] + ".sdk"
 } else {
   sysroot = ""
 }