GN: Add an option to build against the Debian wheezy sysroot

build/config/sysroot.gni

Index: build/config/sysroot.gni
diff --git a/build/config/sysroot.gni b/build/config/sysroot.gni
index 37faae059c3ee5af5cf67180cda341f8840162b5..bb29e6c1340e70af8695f0a1927d02b3665446f5 100644
--- a/build/config/sysroot.gni
+++ b/build/config/sysroot.gni
@@ -9,6 +9,20 @@ declare_args() {
   # The absolute path of the sysroot that is applied when compiling using
   # the target toolchain.
   target_sysroot = ""
+
+  # Whether the Debian wheezy sysroot should be used.
+  dart_use_wheezy_sysroot = false
+}
+
+if (is_linux && dart_use_wheezy_sysroot) {
+  if (current_cpu == "x86") {
+    target_sysroot = rebase_path("//build/linux/debian_wheezy_i386-sysroot")
+  } else if (current_cpu == "x64") {
+    target_sysroot = rebase_path("//build/linux/debian_wheezy_amd64-sysroot")
+  } else {
+    print("There is no Debian wheezy sysroot present for $current_cpu")
+    assert(false)
+  }
 }
 
 if (current_toolchain == default_toolchain && target_sysroot != "") {