Provide missing libz.so for libLLVM

rs/private/rustc_repository.bzl

@@ -7,6 +7,42 @@ load(
 )
 load(":rust_repository_utils.bzl", "RUST_REPOSITORY_COMMON_ATTR", "download_and_extract")
 
+_LINUX_ZLIB = {
+    "aarch64": struct(
+        libdir = "usr/lib/aarch64-linux-gnu",
+        sha256 = "cbe3d39ec32d3cc27c021ae4af11e7c67bdf9d700d573207e0941d4038056278",
+        url = "https://ports.ubuntu.com/ubuntu-ports/pool/main/z/zlib/zlib1g_1.3.dfsg-3.1ubuntu2.1_arm64.deb",
+    ),
+    "x86_64": struct(
+        libdir = "usr/lib/x86_64-linux-gnu",
+        sha256 = "7074b6a2f6367a10d280c00a1cb02e74277709180bab4f2491a2f355ab2d6c20",
+        url = "https://archive.ubuntu.com/ubuntu/pool/main/z/zlib/zlib1g_1.3.dfsg-3.1ubuntu2.1_amd64.deb",
+    ),
+}
+
+def _extract_deb_payload(rctx, url, sha256, output, strip_prefix):
+    deb_dir = ".zlib_deb"
+    rctx.download_and_extract(
+        url = url,
+        sha256 = sha256,
+        output = deb_dir,
+        type = ".deb",
+    )
+
+    data_archive = deb_dir + "/data.tar.zst"
+    if not rctx.path(data_archive).exists:
+        fail("expected data.tar.zst in {}".format(url))
+
+    rctx.extract(data_archive, output = output, stripPrefix = strip_prefix)
+    rctx.delete(deb_dir)
+
+def _add_linux_zlib(rctx, exec_triple):
+    if exec_triple.system != "linux":
+        return
+
+    zlib = _LINUX_ZLIB[exec_triple.arch]
+    _extract_deb_payload(rctx, zlib.url, zlib.sha256, "lib", zlib.libdir)
+
 def _symlink_rust_objcopy_shared_libraries(rctx, exec_triple):
     top_level_lib = rctx.path("lib")
     rustlib_lib = "lib/rustlib/{}/lib".format(exec_triple.str)
@@ -21,6 +57,8 @@ def _symlink_rust_objcopy_shared_libraries(rctx, exec_triple):
 def _rustc_repository_impl(rctx):
     exec_triple = triple(rctx.attr.triple)
     download_and_extract(rctx, "rustc", "rustc", exec_triple)
+    # Upstream Linux rustc bundles libLLVM, which dynamically links against libz.so.1.
+    _add_linux_zlib(rctx, exec_triple)
     _symlink_rust_objcopy_shared_libraries(rctx, exec_triple)
     build_content = [BUILD_for_compiler(
         exec_triple,