Add build_flag_declarations module

And generate build-flags/build_flags.{pb,textproto} files

Bug: 328495189
Test: manual,TH
Change-Id: I97eb864e2d84bc606fef7e9077554894338edaa0
diff --git a/aconfig/build_flags/Android.bp b/aconfig/build_flags/Android.bp
new file mode 100644
index 0000000..69e4316
--- /dev/null
+++ b/aconfig/build_flags/Android.bp
@@ -0,0 +1,23 @@
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+bootstrap_go_package {
+    name: "soong-aconfig-build_flags",
+    pkgPath: "android/soong/aconfig/build_flags",
+    deps: [
+        "blueprint",
+        "blueprint-pathtools",
+        "sbox_proto",
+        "soong",
+        "soong-android",
+    ],
+    srcs: [
+        "all_build_flag_declarations.go",
+        "declarations.go",
+        "init.go",
+    ],
+    testSrcs: [
+    ],
+    pluginFor: ["soong_build"],
+}