support renaming of mangled .rodata sections

When a function foo.isra.1 has a switch statement, it might have a
corresponding .rodata.foo.isra.1 section (in addition to its
.text.foo.isra.1 section).  If so, rename that section too.

I found this bug when trying to build the patch from upstream Linux
commit a3c54931.  Unfortunately this issue is already fixed on F20 and I
wasn't able to come up with a similarly failing test case for the
integration test suite.