A smoke using g++ has revealed:

> KeywordRPN.c: In function 'void XS_XS__APItest__KeywordRPN_import(CV*)':
> KeywordRPN.c:320: error: expected unqualified-id before 'class'
> KeywordRPN.c:320: error: expected initializer before 'class'
> KeywordRPN.c: In function 'void XS_XS__APItest__KeywordRPN_unimport(CV*)':
> KeywordRPN.c:357: error: expected unqualified-id before 'class'
> KeywordRPN.c:357: error: expected initializer before 'class'
> make[1]: *** [KeywordRPN.o] Error 1
> Unsuccessful make(ext/XS-APItest-KeywordRPN): code=512 at make_ext.pl line 449.
> make: *** [lib/auto/XS/APItest/KeywordRPN/KeywordRPN.so] Error 25

I used "class" as a variable name, but in C++ it's a keyword.  Patch
attached.  Someone should also add a note about C++ compatibility to
perlhack.pod.

-zefram