[lldb] Silence warning when building with Clang ToT

This fixes:
```
[6331/7452] Building CXX object tools\lldb\source\Plugins\Language\CPlusPlus\CMakeFiles\lldbPluginCPlusPlusLanguage.dir\LibCxx.cpp.obj
C:\git\llvm-project\lldb\source\Plugins\Language\CPlusPlus\LibCxx.cpp(1108,38): warning: format specifies type 'long' but the argument has type 'std::time_t' (aka 'long long') [-Wformat]
 1108 |     stream.Printf("timestamp=%ld s", seconds);
      |                              ~~~     ^~~~~~~
      |                              %lld
C:\git\llvm-project\lldb\source\Plugins\Language\CPlusPlus\LibCxx.cpp(1116,63): warning: format specifies type 'long' but the argument has type 'std::time_t' (aka 'long long') [-Wformat]
 1116 |     stream.Printf("date/time=%s timestamp=%ld s", str.data(), seconds);
      |                                           ~~~                 ^~~~~~~
      |                                           %lld
2 warnings generated.
```