Add ijar to third_party and use it for generating .jar.toc files in GN

third_party/ijar/BUILD

+package(
+    default_visibility = [
+        "//src:__subpackages__",
+        "//third_party/ijar:__subpackages__",
+    ],
+)
+
+licenses(["notice"])  # Apache 2.0
+
+cc_library(
+    name = "zip",
+    srcs = ["zip.cc"],
+    hdrs = [
+        "common.h",
+        "zip.h",
+    ],
+    # TODO(bazel-team): we should replace the -lz flag, it is non-hermetic.
+    #  We should instead use a new_local_repository once the autoconf
+    #  mechanism is ready.
+    linkopts = ["-lz"],
+)
+
+cc_binary(
+    name = "zipper",
+    srcs = ["zip_main.cc"],
+    visibility = ["//visibility:public"],
+    deps = [":zip"],
+)
+
+cc_binary(
+    name = "ijar",
+    srcs = [
+        "classfile.cc",
+        "ijar.cc",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [":zip"],
+)