Fix Openwrt CC build

[lantis1008]

Fixes due to changes in Openwrt infrastructure arrangements. Depending on how the dust settles, can drop patch 031 (or rework it).

• Bump CC to latest
• Fix (and rework) build script
  • Remove the notion of pulling "trunk". We now set the openwrt_commit to nothing to pull latest from any branch
  • Add ability to specify a branch for packages

We can use this same script with 17.01 reasonably easily with the following example:

-branch_name="Chaos Calmer"
+branch_name="17.01"
-branch_id="chaos_calmer"
+branch_id="openwrt"
-packages_branch="for-15.01"
+packages_branch="lede-17.01"
-openwrt_commit="e6fbf31baae41b618ff333f3ae55ff032333bd6a"
+openwrt_commit="444add156f2a6d92fc15005c5ade2208a978966c"

Patch 031 would need to be dropped in this case.