Fix value history shown for 'gc-cons-percentage'

Fix value history shown for 'gc-cons-percentage'

When Emacs is built, temacs is run in batch mode, so if we enlarge
'gc-cons-percentage' in that case, the enlarged value will be
"remembered" by the dumped Emacs, and will show confusing
information in "C-h v", claiming that the original value was 1.0.
Keeping the value at 0.1 during dumping avoids that.

* src/emacs.c (main): Increase 'gc-cons-percentage' in batch mode
only if we are not initializing (a.k.a. "dumping") Emacs.