Clean up some GN toolchain args, especially NaCl.

build/toolchain/nacl_toolchain.gni

Index: build/toolchain/nacl_toolchain.gni
diff --git a/build/toolchain/nacl_toolchain.gni b/build/toolchain/nacl_toolchain.gni
index ab3b693a142e3f5575a46e0fd71a2aa2c3c9cc12..d9ab77d23a5068ea6b38669c16227add0293facf 100644
--- a/build/toolchain/nacl_toolchain.gni
+++ b/build/toolchain/nacl_toolchain.gni
@@ -22,36 +22,32 @@ template("nacl_toolchain") {
   assert(defined(invoker.ld), "nacl_toolchain() must specify a \"ld\" value")
   assert(defined(invoker.toolchain_cpu),
          "nacl_toolchain() must specify a \"toolchain_cpu\"")
+  gcc_toolchain(target_name) {
+    toolchain_os = "nacl"
 
-  toolchain_os = "nacl"
-  if (defined(invoker.is_clang)) {
-    is_clang = invoker.is_clang
-  }
-  if (defined(invoker.executable_extension)) {
-    executable_extension = invoker.executable_extension
-  } else {
-    executable_extension = ".nexe"
-  }
-  toolchain_cpu = invoker.toolchain_cpu
+    if (defined(invoker.executable_extension)) {
+      executable_extension = invoker.executable_extension
+    } else {
+      executable_extension = ".nexe"
+    }
 
-  cc = invoker.cc
-  cxx = invoker.cxx
-  ar = invoker.ar
-  ld = invoker.ld
-  if (defined(invoker.postlink)) {
-    postlink = invoker.postlink
-  }
-  if (defined(invoker.link_outputs)) {
-    link_outputs = invoker.link_outputs
-  }
+    forward_variables_from(invoker,
+                           [
+                             "ar",
+                             "cc",
+                             "cxx",
+                             "deps",
+                             "is_clang",
+                             "ld",
+                             "link_outputs",
+                             "postlink",
+                             "toolchain_cpu",
+                           ])
 
-  # We do not wish to suport shared builds with the NaCl toolchains.
-  is_component_build = false
+    # We do not suport component builds or sanitizers with the NaCl toolchains.
+    is_component_build = false
+    clear_sanitizers = true
 
-  gcc_toolchain(target_name) {
     rebuild_define = "NACL_TC_REV=" + invoker.toolchain_revision
-    if (defined(invoker.deps)) {
-      deps = invoker.deps
-    }
   }
 }