middle-end/110489 - avoid useless work on statistics

When we call statistics_fini_pass we unconditionally allocate
the statistics hash and traverse it.  When a TU has many small
functions this can take considerable time.  The following avoids
this by never allocating the hash from this function.

	PR middle-end/110489
	* statistics.cc (curr_statistics_hash): Add argument
	indicating whether we should allocate the hash.
	(statistics_fini_pass): If the hash isn't allocated
	only print the summary header.