Move ELF build-id reader into a separate library.

Bug: 328702178
Change-Id: I188a8d20d22e67e4f0c7e3441e3781fff369c828
diff --git a/cmd/symbols_map/Android.bp b/cmd/symbols_map/Android.bp
index 0ba3b07..e3ae6ed 100644
--- a/cmd/symbols_map/Android.bp
+++ b/cmd/symbols_map/Android.bp
@@ -5,17 +5,16 @@
 blueprint_go_binary {
     name: "symbols_map",
     srcs: [
-        "elf.go",
         "r8.go",
         "symbols_map.go",
     ],
     testSrcs: [
-        "elf_test.go",
         "r8_test.go",
     ],
     deps: [
         "blueprint-pathtools",
         "golang-protobuf-encoding-prototext",
+        "soong-elf",
         "soong-response",
         "symbols_map_proto",
     ],