avoid use of defined-or to support older Perls
duplicate symbol error

removed duplicate declarations in .xs for some Triangle global
variables, except for the one needed, and set that to extern.
Duplicate symbol error only came up in mac compile environment.
compiler flag to get 64bit long under 64 bit MinGW

Triangle assumes that unsigned long is big enough to hold a
pointer. On 64 bit windows it's not. The gcc -m64 switch was
added to fix this under MinGW (Citrus/Strawberry Perl).
new version