Add libgmp 6.2.0 to third_party

Don't build it yet.  That will come in the next review.

Change-Id: Idf3266558165e5ab45f4a41c98cc8c838c8244d5
diff --git a/third_party/gmp/scanf/fscanffuns.c b/third_party/gmp/scanf/fscanffuns.c
new file mode 100644
index 0000000..f2d2939
--- /dev/null
+++ b/third_party/gmp/scanf/fscanffuns.c
@@ -0,0 +1,61 @@
+/* __gmp_fscanf_funs -- support for formatted input from a FILE.
+
+   THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY.  THEY'RE ALMOST
+   CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
+   FUTURE GNU MP RELEASES.
+
+Copyright 2001 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of either:
+
+  * the GNU Lesser General Public License as published by the Free
+    Software Foundation; either version 3 of the License, or (at your
+    option) any later version.
+
+or
+
+  * the GNU General Public License as published by the Free Software
+    Foundation; either version 2 of the License, or (at your option) any
+    later version.
+
+or both in parallel, as here.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received copies of the GNU General Public License and the
+GNU Lesser General Public License along with the GNU MP Library.  If not,
+see https://www.gnu.org/licenses/.  */
+
+#include <stdio.h>
+#include "gmp-impl.h"
+
+
+/* SunOS 4 stdio.h doesn't provide prototypes for these */
+#if ! HAVE_DECL_FGETC
+int fgetc (FILE *);
+#endif
+#if ! HAVE_DECL_FSCANF
+int fscanf (FILE *, const char *, ...);
+#endif
+#if ! HAVE_DECL_UNGETC
+int ungetc (int, FILE *);
+#endif
+
+
+static void
+step (FILE *fp, int n)
+{
+}
+
+const struct gmp_doscan_funs_t  __gmp_fscanf_funs = {
+  (gmp_doscan_scan_t)  fscanf,
+  (gmp_doscan_step_t)  step,
+  (gmp_doscan_get_t)   fgetc,
+  (gmp_doscan_unget_t) ungetc,
+};