remove an EXTEND from XS_re_regexp_pattern

remove an EXTEND from XS_re_regexp_pattern

Replace 2 EXTENDs with 1. Whether the stack is extended by 1 or 2 makes
no signifigant memory difference, so use the large value of 2. Less
machine code is the purpose. This XSUB went from 0x1C2 long to 0x19E for me
after these changes on VC 2003 x86 32bit. The SP and items was moved so
items is tossed a tiny bit sooner by the compiler in case the compiler
tries to save it because it doesn't recogize noreturn declared funcs.