Install libffi-devel to build i868 wheels

Author: jlaine

scripts/build-libsrtp.py

@@ -28,6 +28,9 @@ def run(cmd):
     "-DCMAKE_VERBOSE_MAKEFILE:BOOL=ON",
     "-DENABLE_OPENSSL=ON",
 ]
+if platform.system() == "Linux" and platform.machine() == "i686":
+    # There are no binary wheels for cffi on i686 anymore.
+    run(["yum", "install", "libffi-devel"])
 if platform.system() == "Darwin" and "ARCHFLAGS" in os.environ:
     archs = [x for x in os.environ["ARCHFLAGS"].split() if x != "-arch"]
     cmake_args.append("-DCMAKE_OSX_ARCHITECTURES=" + ";".join(archs))