Fix FTBFS.

Box2D.spec

@@ -1,6 +1,7 @@
+%global __cmake_in_source_build 1
 Name: Box2D
 Version:  2.3.1
-Release:  14%{?dist}
+Release:  15%{?dist}
 Summary: A 2D Physics Engine for Games
 
 License: zlib
@@ -69,6 +70,9 @@ find %{buildroot} -name '*.a' | xargs rm
 
 
 %changelog
+* Tue Aug 04 2020 Gwyn Ciesla <gwync@protonmail.com> - 2.3.1-15
+- Fix FTBFS.
+
 * Sat Aug 01 2020 Fedora Release Engineering <releng@fedoraproject.org> - 2.3.1-14
 - Second attempt - Rebuilt for
   https://fedoraproject.org/wiki/Fedora_33_Mass_Rebuild