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/mpn/powerpc32/umul.asm b/third_party/gmp/mpn/powerpc32/umul.asm
new file mode 100644
index 0000000..a5811e1
--- /dev/null
+++ b/third_party/gmp/mpn/powerpc32/umul.asm
@@ -0,0 +1,50 @@
+dnl  PowerPC-32 umul_ppmm -- support for longlong.h
+
+dnl  Copyright 2000, 2001 Free Software Foundation, Inc.
+
+dnl  This file is part of the GNU MP Library.
+dnl
+dnl  The GNU MP Library is free software; you can redistribute it and/or modify
+dnl  it under the terms of either:
+dnl
+dnl    * the GNU Lesser General Public License as published by the Free
+dnl      Software Foundation; either version 3 of the License, or (at your
+dnl      option) any later version.
+dnl
+dnl  or
+dnl
+dnl    * the GNU General Public License as published by the Free Software
+dnl      Foundation; either version 2 of the License, or (at your option) any
+dnl      later version.
+dnl
+dnl  or both in parallel, as here.
+dnl
+dnl  The GNU MP Library is distributed in the hope that it will be useful, but
+dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+dnl  for more details.
+dnl
+dnl  You should have received copies of the GNU General Public License and the
+dnl  GNU Lesser General Public License along with the GNU MP Library.  If not,
+dnl  see https://www.gnu.org/licenses/.
+
+include(`../config.m4')
+
+
+C mp_limb_t mpn_umul_ppmm (mp_limb_t *lowptr, mp_limb_t m1, mp_limb_t m2);
+C
+
+ASM_START()
+PROLOGUE(mpn_umul_ppmm)
+
+	C r3	lowptr
+	C r4	m1
+	C r5	m2
+
+	mullw	r0, r4, r5
+	mulhwu	r9, r4, r5
+	stw	r0, 0(r3)
+	mr	r3, r9
+	blr
+
+EPILOGUE(mpn_umul_ppmm)