Building gdextensions with lto=full warns about serial compilaton

### Godot version

4.6

### godot-cpp version

3a7edf0

### System information

Arch Linux

### Issue description

Building GD extensions with the 'lto=full' flag produces the following warning
```
warning: using serial compilation of 10 LTRANS jobs
lto-wrapper: note: see the '-flto' option documentation for more information
```
Which slows down compilation times.

After some research the warning appears due to a change in the -flto option introduced in GCC 11.4. The -flto option only uses parallel compilation if explicitly instructed to do so. By default, it uses slow serial compilation. updating "common_compiler_flags.py" to change instances of '-flto' to '-flto=auto' will re-enable parallelization.

### Steps to reproduce

Compile any GD Extension with ```scons lto=full```

### Minimal reproduction project

N/A