simplify zig build workaround

From ziglang/zig#14815 (comment):

> @motiejus to be clear, this unrelated issue is not affected by a cache
> clear, and can be resolved by simply rerunning the build (and not
> getting very unlucky again).

toolchain/defs.bzl

@@ -54,14 +54,14 @@ stderr={stderr}
 stdout={stdout}
 
 You stumbled into a problem with Zig SDK that bazel-zig-cc was not able to fix.
-Please file a new issue to github.com/uber/bazel-zig-cc with:
+Please file a new issue to github.com/uber/hermetic_cc_toolchain with:
 - Full output of this Bazel run, including the Bazel command.
 - Version of the Zig SDK if you have a non-default.
-- Version of bazel-zig-cc.
+- Version of hermetic_cc_toolchain
 
-Note: this *may* have been https://github.com/ziglang/zig/issues/14815, for
-which bazel-zig-cc has a workaround and you may have been "struck by lightning"
-three times in a row.
+Note: this *may* have been https://github.com/ziglang/zig/issues/14978, for
+which hermetic_cc_toolchain has a workaround and you may have been "struck by
+lightning" three times in a row.
 """
 
 def toolchains(
@@ -129,7 +129,6 @@ def _zig_repository_impl(repository_ctx):
 
     for dest, src in {
         "BUILD": "//toolchain:BUILD.sdk.bazel",
-        # "private/BUILD": "//toolchain/private:BUILD.sdk.bazel",
     }.items():
         repository_ctx.template(
             dest,
@@ -177,27 +176,13 @@ def _zig_repository_impl(repository_ctx):
         "launcher.zig",
     ] + (["-static"] if os == "linux" else [])
 
-    # The elaborate code below is a workaround for ziglang/zig#14815:
-    # Sometimes, when Zig's cache is empty, compiling the launcher may fail
-    # with `error: FileNotFound`. The remedy is to clear the cache and try
-    # again. Until this change, we have been asking users to clear the Zig
-    # cache themselves and re-run the Bazel command.
-    #
-    # We can do better than that: if we detect the launcher failed, we can
-    # purge the zig cache and retry the compilation. It will be retried for up
-    # to two times.
+    # The elaborate code below is a workaround for ziglang/zig#14978: a race in
+    # Windows where zig may error with `error: AccessDenied`.
     launcher_success = True
     launcher_err_msg = ""
     for _ in range(3):
-        # Do not remove the cache_prefix itself, because it is not controlled
-        # by this script. Instead, clear the cache subdirs that we know Zig
-        # populates.
-        zig_cache_dirs = ["h", "o", "tmp", "z"]
         if not launcher_success:
-            print("Launcher compilation failed. Clearing %s/{%s} and retrying" %
-                  (cache_prefix, ",".join(zig_cache_dirs)))
-            for d in zig_cache_dirs:
-                repository_ctx.delete(_paths_join(cache_prefix, d))
+            print("Launcher compilation failed. Retrying build")
 
         ret = repository_ctx.execute(
             compile_cmd,