* configure.ac: Check for chsize and posix_fallocate. Replace

ftruncate.
	* ftruncate.c: New file, from gnulib.
	* output.cc (posix_fallocate): Define dummy version if not
	HAVE_POSIX_FALLOCATE.
	(Output_file::map): Call posix_fallocate rather than lseek and
	write.
	* gold.h (ftruncate): Declare if not HAVE_FTRUNCATE.
	* configure, Makefile.in, config.in: Rebuild.

gold/ftruncate.c

@@ -0,0 +1,90 @@
+/* ftruncate emulations that work on some System V's.
+   This file is in the public domain.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <unistd.h>
+
+#include <sys/types.h>
+#include <fcntl.h>
+
+#ifdef F_CHSIZE
+
+int
+ftruncate (int fd, off_t length)
+{
+  return fcntl (fd, F_CHSIZE, length);
+}
+
+#else /* not F_CHSIZE */
+# ifdef F_FREESP
+
+/* By William Kucharski <kucharsk@netcom.com>.  */
+
+#  include <sys/stat.h>
+#  include <errno.h>
+
+int
+ftruncate (int fd, off_t length)
+{
+  struct flock fl;
+  struct stat filebuf;
+
+  if (fstat (fd, &filebuf) < 0)
+    return -1;
+
+  if (filebuf.st_size < length)
+    {
+      /* Extend file length. */
+      if (lseek (fd, (length - 1), SEEK_SET) < 0)
+	return -1;
+
+      /* Write a "0" byte. */
+      if (write (fd, "", 1) != 1)
+	return -1;
+    }
+  else
+    {
+
+      /* Truncate length. */
+
+      fl.l_whence = 0;
+      fl.l_len = 0;
+      fl.l_start = length;
+      fl.l_type = F_WRLCK;	/* write lock on file space */
+
+      /* This relies on the *undocumented* F_FREESP argument to fcntl,
+	 which truncates the file so that it ends at the position
+	 indicated by fl.l_start.  Will minor miracles never cease?  */
+
+      if (fcntl (fd, F_FREESP, &fl) < 0)
+	return -1;
+    }
+
+  return 0;
+}
+
+# else /* not F_CHSIZE nor F_FREESP */
+#  if HAVE_CHSIZE                      /* native Windows, e.g. mingw */
+
+int
+ftruncate (int fd, off_t length)
+{
+  return chsize (fd, length);
+}
+
+#  else /* not F_CHSIZE nor F_FREESP nor HAVE_CHSIZE */
+
+#   include <errno.h>
+
+int
+ftruncate (int fd, off_t length)
+{
+  errno = EIO;
+  return -1;
+}
+
+#  endif /* not HAVE_CHSIZE */
+# endif /* not F_FREESP */
+#endif /* not F_CHSIZE */