Convert ImageMagick to Soong

See build/soong/README.md for more information.

Test: cd external/ImageMagick; mma
Change-Id: Ide3c1556c3825c4b115a3189aabc48f3dc5782e9
diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..d8d913a
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,5 @@
+cc_library_headers {
+    name: "Magick_headers",
+    export_include_dirs: ["."],
+    sdk_version: "24",
+}