* configure.ac: Check for sys/mman.h and mmap. Check for mremap

	* configure.ac: Check for sys/mman.h and mmap.  Check for mremap
	with MREMAP_MAYMOVE.
	* output.h (class Output_file): Add map_is_allocated_ field.
	* output.cc: Only #include <sys/mman.h> if it exists.  If mmap is
	not available, provide stubs.  If mremap is not available, #define
	it to gold_mremap.
	(MREMAP_MAYMOVE): Define if not defined.
	(Output_file::Output_file): Initialize map_is_allocated_.
	(Output_file::resize): Check map_is_allocated_.
	(Output_file::map_anonymous): If mmap fails, use malloc.
	(Output_file::unmap): Don't do anything for an anonymous map.
	* fileread.cc: Only #include <sys/mman.h> if it exists.  If mmap
	is not available, provide stubs.
	(File_read::View::~View): Use free rather than delete[].
	(File_read::make_view): Use malloc rather than new[].  If mmap
	fails, use malloc.
	(File_read::find_or_make_view): Use malloc rather than new[].
	* gold.h: Remove HAVE_REMAP code.
	* mremap.c: #include <errno.h>.  Only #include <sys/mman.h> if it
	exists.  Rename mremap to gold_mremap.  If mmap is not available
	don't do anything.
	* configure, config.in: Rebuild.