Log Message:
Changes 2.0.10:

Declare MP_vtbl_env and MP_vtbl_envelem as 'extern' to fix linker errors on
OSX/Darwin.

Automatically select the appropriate c89 option when modperl is being
built with either gcc 5 or clang.

Fix non-threaded Perl 5.22.x build and tests.

Add support for Perl 5.22.x.