[scripts] Add script to print clang prebuilts version

Bug: http://b/187231324

This script parses soong/cc/config/global.go to return clang prebuilts
version.  (It may get the version from a json config file in the
future.)

Currently it's used in development/scripts/symbol.py and is the
recommended way to get clang prebuilts version number in the future.

Test: get_clang_version_test.py
Change-Id: Id92a74fd523a5270999bb4d6454525bf2f2f0c04

Android.bp

@@ -116,3 +116,13 @@ cc_genrule {
 dex_bootjars {
     name: "dex_bootjars",
 }
+
+// Pseudo-test that's run on checkbuilds to ensure that get_clang_version can
+// parse cc/config/global.go.
+genrule {
+    name: "get_clang_version_test",
+    cmd: "$(location get_clang_version) > $(out)",
+    tools: ["get_clang_version"],
+    srcs: ["cc/config/global.go"],
+    out: ["clang-prebuilts-version.txt"],
+}