project.conf: Use variables and options from freedesktop-sdk

This way we can use variables like 'gcc_triplet'

project.conf

@@ -29,3 +29,21 @@ plugins:
 
 aliases:
   github: https://github.com/
+
+options:
+  # Copied from Freedesktop SDK (Shouldn't be junctioned)
+  target_arch:
+    type: arch
+    description: Architecture
+    variable: arch
+    values:
+      - arm
+      - aarch64
+      - i686
+      - x86_64
+      - powerpc64le
+
+variables:
+  (@):
+  - freedesktop-sdk.bst:include/arch.yml
+  - freedesktop-sdk.bst:include/build-flags.yml