Remove calls to tmpnam() in protobuf/testing/googletest.cc.

This came up as a pull request here:
#18239.

|tmpnam| is ugly and would be nice to avoid.

We don't necessarily want to substitute out GetTemporaryDirectoryName with
|std::filesystem::temp_directory_path| -- the current setup creates a
subdirectory under the tmp directory and uses TempDirDeleter to clean it up.
We want to preserve that behaviour: the current setup plays nicely with bazel
without polluting /tmp with unbounded growth.

#test-continuous

PiperOrigin-RevId: 677843997

src/google/protobuf/testing/googletest.cc

@@ -22,6 +22,8 @@
 #include "absl/strings/str_replace.h"
 #include "google/protobuf/io/io_win32.h"
 #include "google/protobuf/testing/file.h"
+#include <gtest/gtest.h>
+
 #ifdef _MSC_VER
 // #include <direct.h>
 #else
@@ -93,45 +95,8 @@ std::string TestSourceDir() {
 namespace {
 
 std::string GetTemporaryDirectoryName() {
-  // Tests run under Bazel "should not" use /tmp. Bazel sets this environment
-  // variable for tests to use instead.
-  char* from_environment = getenv("TEST_TMPDIR");
-  if (from_environment != nullptr && from_environment[0] != '\0') {
-    return absl::StrCat(from_environment, "/protobuf_tmpdir");
-  }
-
-  // tmpnam() is generally not considered safe but we're only using it for
-  // testing.  We cannot use tmpfile() or mkstemp() since we're creating a
-  // directory.
-  char b[L_tmpnam + 1];     // HPUX multithread return 0 if s is 0
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-  std::string result = tmpnam(b);
-#pragma GCC diagnostic pop
+  std::string result = absl::StrCat(testing::TempDir(), "protobuf_tempdir");
 #ifdef _WIN32
-  // Avoid a trailing dot by changing it to an underscore. On Win32 the names of
-  // files and directories can, but should not, end with dot.
-  //
-  // In MS-DOS and FAT16 filesystem the filenames were 8dot3 style so it didn't
-  // make sense to have a name ending in dot without an extension, so the shell
-  // silently ignored trailing dots. To this day the Win32 API still maintains
-  // this behavior and silently ignores trailing dots in path arguments of
-  // functions such as CreateFile{A,W}. Even POSIX API function implementations
-  // seem to wrap the Win32 API functions (e.g. CreateDirectoryA) and behave
-  // this way.
-  // It's possible to avoid this behavior and create files / directories with
-  // trailing dots (using CreateFileW / CreateDirectoryW and prefixing the path
-  // with "\\?\") but these will be degenerate in the sense that you cannot
-  // chdir into such directories (or navigate into them with Windows Explorer)
-  // nor can you open such files with some programs (e.g. Notepad).
-  if (result[result.size() - 1] == '.') {
-    result[result.size() - 1] = '_';
-  }
-  // On Win32, tmpnam() returns a file prefixed with '\', but which is supposed
-  // to be used in the current working directory.  WTF?
-  if (absl::StartsWith(result, "\\")) {
-    result.erase(0, 1);
-  }
   // The Win32 API accepts forward slashes as a path delimiter as long as the
   // path doesn't use the "\\?\" prefix.
   // Let's avoid confusion and use only forward slashes.