Ignore read-only errors when updating the mtime of the install_base

Currently if the `--install_base` path passed is not writable by the
user invoking Bazel, the Bazel client crashes[^1]:
```console
❯ bazel --install_base=/some/read/only/path version
FATAL: failed to set timestamp on '/some/read/only/path': (error: 30): Read-only file system
```

This happens because the Bazel client (unconditionally) attempts to
update the `mtime` of this path:
https://github.com/bazelbuild/bazel/blob/a3c677dfea2de636a719d50345a5a97af96fae60/src/main/cpp/blaze.cc#L1018-L1029

This commit updates the client to ignore such errors. See bazelbuild#20373 for
context.

src/main/cpp/blaze.cc

@@ -59,6 +59,12 @@
 #include <unistd.h>
 #endif
 
+#if !defined(_WIN32)
+#include <cerrno>
+#else
+#include <windows.h>
+#endif
+
 #include "src/main/cpp/archive_utils.h"
 #include "src/main/cpp/blaze_util.h"
 #include "src/main/cpp/blaze_util_platform.h"
@@ -1012,10 +1018,24 @@ static void EnsureCorrectRunningVersion(const StartupOptions &startup_options,
     std::unique_ptr<blaze_util::IFileMtime> mtime(
         blaze_util::CreateFileMtime());
     if (!mtime->SetToNow(blaze_util::Path(startup_options.install_base))) {
-      string err = GetLastErrorString();
-      BAZEL_DIE(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR)
-          << "failed to set timestamp on '" << startup_options.install_base
-          << "': " << err;
+      // Ignore permissions errors (i.e. if the install base is not writable):
+      bool raise_error = true;
+
+#if defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__APPLE__) || defined(__CYGWIN__)
+      // On POSIX platforms, `SetToNow` is backed by `utime(2)` which can
+      // return `EROFS`/`EPERM`:
+      if (errno == EROFS || errno == EPERM) { raise_error = false; }
+#elif defined(_WIN32)
+      // On Windows, `SetToNow` is backed by `CreateFileW` + `SetFileTime`:
+      if (::GetLastError() == ERROR_ACCESS_DENIED) { raise_error = false; }
+#endif
+
+      if (raise_error) {
+        string err = GetLastErrorString();
+        BAZEL_DIE(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR)
+            << "failed to set timestamp on '" << startup_options.install_base
+            << "': " << err;
+      }
     }
   }
 }