Revert "Remove gmp from AOS"

This reverts commit f37c97684f0910a3f241394549392f00145ab0f7.

We need gmp for SymEngine for symbolicmanipultion in C++

Change-Id: Ia13216d1715cf96944f7b4f422b7a799f921d4a4
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/third_party/gmp/mpz/get_si.c b/third_party/gmp/mpz/get_si.c
new file mode 100644
index 0000000..c65be2e
--- /dev/null
+++ b/third_party/gmp/mpz/get_si.c
@@ -0,0 +1,52 @@
+/* mpz_get_si(integer) -- Return the least significant digit from INTEGER.
+
+Copyright 1991, 1993-1995, 2000-2002, 2006, 2012 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 "gmp-impl.h"
+
+signed long int
+mpz_get_si (mpz_srcptr z) __GMP_NOTHROW
+{
+  mp_ptr zp = PTR (z);
+  mp_size_t size = SIZ (z);
+  mp_limb_t zl = zp[0];
+
+#if GMP_NAIL_BITS != 0
+  if (ULONG_MAX > GMP_NUMB_MAX && ABS (size) >= 2)
+    zl |= zp[1] << GMP_NUMB_BITS;
+#endif
+
+  if (size > 0)
+    return zl & LONG_MAX;
+  else if (size < 0)
+    /* This expression is necessary to properly handle 0x80000000 */
+    return -1 - (long) ((zl - 1) & LONG_MAX);
+  else
+    return 0;
+}