gcov: use mmap pools for KVP.

gcc/ChangeLog:

	PR gcov-profile/97461
	* gcov-io.h (GCOV_PREALLOCATED_KVP): Remove.

libgcc/ChangeLog:

	PR gcov-profile/97461
	* config.in: Regenerate.
	* configure: Likewise.
	* configure.ac: Check sys/mman.h header file
	* libgcov-driver.c (struct gcov_kvp): Remove static
	pre-allocated pool and use a dynamic one.
	* libgcov.h (MMAP_CHUNK_SIZE): New.
	(gcov_counter_add): Use mmap to allocate pool for struct
	gcov_kvp.