Allow projects to define their own build.

To create a new project, add a directory under `project` and pass the
project name to `make`:

    mkdir project/my_project
    # Describe the build for the project.
    PROJECT=my_project make

Projects can be maintained separately from the main repository.

Change-Id: I33a9d7ca801e2fb3dd9795ece44577b3b565e913
diff --git a/build/toolchain/embedded.gni b/build/toolchain/embedded.gni
index b9a5cdd..290f163 100644
--- a/build/toolchain/embedded.gni
+++ b/build/toolchain/embedded.gni
@@ -185,9 +185,11 @@
     extra_cflags = cflags
     extra_ldflags = ldflags
     toolchain_args = {
-      platform_max_cpus = invoker.max_cpus
-      platform_max_vms = invoker.max_vms
-      arch = invoker.arch
+      use_platform = true
+      plat_name = invoker.target_name
+      plat_arch = invoker.arch
+      plat_max_cpus = invoker.max_cpus
+      plat_max_vms = invoker.max_vms
       if (defined(invoker.toolchain_args)) {
         forward_variables_from(invoker.toolchain_args, "*")
       }
@@ -200,9 +202,11 @@
     extra_cflags = cflags
     extra_ldflags = ldflags
     toolchain_args = {
-      platform_max_cpus = invoker.max_cpus
-      platform_max_vms = invoker.max_vms
-      arch = invoker.arch
+      use_platform = true
+      plat_name = invoker.target_name
+      plat_arch = invoker.arch
+      plat_max_cpus = invoker.max_cpus
+      plat_max_vms = invoker.max_vms
       if (defined(invoker.toolchain_args)) {
         forward_variables_from(invoker.toolchain_args, "*")
       }