Minor fix to connect-url to support unix-connect sockets on localhost (#142875)

**Summary:**

when the unix-socket connections on localhost are used to for platform
connect i.e.
`platform connect unix-connect:///path/to/socket.sock`
then `PlatformRemoteGDBServer.m_platform_hostname` is empty.

Based on the current logic, for the process attach, when the connection
param returned by platform server as qLaunchGDBServer is this
`socket_name:/path/to/processgdbserver.sock`
then the subsequent connect url for the process url looks like this
`unix-connect://[]/path/to/processgdbserver.sock` and the connection
fail.

This change is only adding the braces when the hostname is not empty.

**Test Plan:**

Added unittest and existing tests pass.
```
satyajanga@devvm21837:toolchain $ LLDB_COMMAND_TRACE=YES ./bin/llvm-lit --verbose  ~/llvm-sand/external/llvm-project/lldb/test/API/commands/platform
-- Testing: 9 tests, 9 workers --
UNSUPPORTED: lldb-api :: commands/platform/sdk/TestPlatformSDK.py (1 of 9)
PASS: lldb-api :: commands/platform/file/read/TestPlatformFileRead.py (2 of 9)
PASS: lldb-api :: commands/platform/file/close/TestPlatformFileClose.py (3 of 9)
PASS: lldb-api :: commands/platform/basic/TestPlatformPython.py (4 of 9)
PASS: lldb-api :: commands/platform/basic/TestPlatformCommand.py (5 of 9)
PASS: lldb-api :: commands/platform/process/launch/TestPlatformProcessLaunch.py (6 of 9)
PASS: lldb-api :: commands/platform/connect/TestPlatformConnect.py (7 of 9)
PASS: lldb-api :: commands/platform/launchgdbserver/TestPlatformLaunchGDBServer.py (8 of 9)
PASS: lldb-api :: commands/platform/process/list/TestProcessList.py (9 of 9)

Testing Time: 13.24s

Total Discovered Tests: 9
  Unsupported: 1 (11.11%)
  Passed     : 8 (88.89%)
satyajanga@devvm21837:toolchain $ 

```


Reviewers:

@clayborg 
@Jlalond 

Subscribers:

Tasks:

Tags:

Author: satyajanga

lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.cpp

@@ -800,7 +800,10 @@ std::string PlatformRemoteGDBServer::MakeUrl(const char *scheme,
                                              const char *hostname,
                                              uint16_t port, const char *path) {
   StreamString result;
-  result.Printf("%s://[%s]", scheme, hostname);
+  result.Printf("%s://", scheme);
+  if (strlen(hostname) > 0)
+    result.Printf("[%s]", hostname);
+
   if (port != 0)
     result.Printf(":%u", port);
   if (path)

lldb/test/API/commands/platform/connect/TestPlatformConnect.py

@@ -57,3 +57,48 @@ def test_platform_process_connect(self):
         self.assertEqual(frame.GetFunction().GetName(), "main")
         self.assertEqual(frame.FindVariable("argc").GetValueAsSigned(), 2)
         process.Continue()
+
+    @skipIfRemote
+    @expectedFailureAll(hostoslist=["windows"], triple=".*-android")
+    @skipIfDarwin  # lldb-server not found correctly
+    @expectedFailureAll(oslist=["windows"])  # process modules not loaded
+    # lldb-server platform times out waiting for the gdbserver port number to be
+    # written to the pipe, yet it seems the gdbserver already has written it.
+    @expectedFailureAll(
+        archs=["aarch64"],
+        oslist=["freebsd"],
+        bugnumber="https://github.com/llvm/llvm-project/issues/84327",
+    )
+    @add_test_categories(["lldb-server"])
+    def test_platform_process_connect_with_unix_connect(self):
+        self.build()
+        lldb_temp_dir = lldb.SBHostOS.GetLLDBPath(lldb.ePathTypeLLDBTempSystemDir)
+        named_pipe = "%s/platform_server.sock" % lldb_temp_dir
+        port_file = self.getBuildArtifact("port")
+        commandline_args = [
+            "platform",
+            "--listen",
+            named_pipe,
+            "--socket-file",
+            port_file,
+            "--",
+            self.getBuildArtifact("a.out"),
+            "foo",
+        ]
+        self.spawnSubprocess(lldbgdbserverutils.get_lldb_server_exe(), commandline_args)
+
+        socket_file = lldbutil.wait_for_file_on_target(self, port_file)
+        new_platform = lldb.SBPlatform("remote-" + self.getPlatform())
+        self.dbg.SetSelectedPlatform(new_platform)
+        connect_url = "unix-connect://%s" % socket_file
+        self.runCmd("platform connect %s" % connect_url)
+
+        lldbutil.run_break_set_by_symbol(self, "main")
+        process = self.process()
+
+        process.Continue()
+
+        frame = self.frame()
+        self.assertEqual(frame.GetFunction().GetName(), "main")
+        self.assertEqual(frame.FindVariable("argc").GetValueAsSigned(), 2)
+        process.Continue()