Add -32bit patch to fix build on 32-bit platforms.

ocaml-mlmpfr-32bit.patch

@@ -0,0 +1,11 @@
+--- src/mlmpfr_stubs.c.orig	2019-11-03 01:49:34.000000000 -0700
++++ src/mlmpfr_stubs.c	2020-03-25 10:57:18.279258620 -0600
+@@ -39,7 +39,7 @@ precision_in_range (value prec)
+   int p = Int_val (prec);
+ 
+   if (p <= Int_val (caml_mpfr_prec_min ())
+-      || p >= Int_val (caml_mpfr_prec_max ()))
++      || p >= Unsigned_int_val (caml_mpfr_prec_max ()))
+     caml_raise_with_arg (*caml_named_value ("precision range exception"),
+                          Val_int (p));
+ }

ocaml-mlmpfr.spec

@@ -8,6 +8,8 @@ Summary:        OCaml bindings for MPFR
 License:        LGPLv3
 URL:            https://github.com/thvnx/%{srcname}
 Source0:        %{url}/archive/%{srcname}.%{version}-dune.tar.gz
+# Fix integer overflow on 32-bit architectures
+Patch0:         %{name}-32bit.patch
 
 BuildRequires:  ocaml >= 4.04
 BuildRequires:  ocaml-dune >= 1.11.0
@@ -34,7 +36,7 @@ BuildArch:      noarch
 Documentation for %{name}.
 
 %prep
-%autosetup -n %{srcname}-%{srcname}.%{version}-dune
+%autosetup -n %{srcname}-%{srcname}.%{version}-dune -p0
 
 %build
 dune build %{?_smp_mflags}