Use MADV_DONTNEED for freeing in garbage collector

Use MADV_DONTNEED for freeing in garbage collector

Use the Linux MADV_DONTNEED call to unmap free pages in the garbage
collector.Then keep the unmapped pages in the free list. This avoid
excessive memory fragmentation on large LTO bulds, which can lead
to gcc bumping into the Linux vm_max_map limit per process.

gcc/:

2011-10-08  Andi Kleen  <ak@linux.intel.com>

	PR other/50636
	* config.in, configure: Regenerate.
	* configure.ac (madvise): Add to AC_CHECK_FUNCS.
	* ggc-page.c (USING_MADVISE): Add.
	(page_entry): Add discarded field.
	(alloc_page): Check for discarded pages.
	(release_pages): Add USING_MADVISE branch.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@180093 138bc75d-0d04-0410-961f-82ee72b054a4