Add -clear-err patch to fix a sympy test case.

gmpy2-clear-err.patch

@@ -0,0 +1,10 @@
+--- src/gmpy2_mpz_misc.c.orig	2018-04-14 12:27:51.000000000 -0600
++++ src/gmpy2_mpz_misc.c	2018-07-12 11:07:36.053833908 -0600
+@@ -795,6 +795,7 @@ GMPy_MPZ_Function_Bincoef(PyObject *self
+         return (PyObject*)result;
+     }
+ 
++    PyErr_Clear();
+     if (!(tempx = GMPy_MPZ_From_Integer(PyTuple_GET_ITEM(args, 0), NULL))) {
+         Py_DECREF((PyObject*)result);
+         return NULL;

python-gmpy2.spec

@@ -16,6 +16,8 @@ Source0:        https://github.com/aleaxit/gmpy/archive/%{srcname}-%{version}a2.
 Patch0:         %{srcname}-import.patch
 # Fix adding by zero in place; https://github.com/aleaxit/gmpy/issues/200
 Patch1:         %{srcname}-addzero.patch
+# Fix spurious overlow error in bincoef
+Patch2:         %{srcname}-clear-err.patch
 
 BuildRequires:  gcc
 BuildRequires:  gmp-devel
@@ -73,6 +75,7 @@ mv gmpy-%{srcname}-%{version}a2 python2
 pushd python2
 %patch0
 %patch1
+%patch2
 
 # Fix file encodings.  First the easy one.
 iconv -f ISO8859-1 -t UTF-8 src/gmpy2.c > src/gmpy2.c.utf8