To fix cygwin and probably windows also:
src/resources.c:64: error: external linkage required for symbol 'end_locker' because of 'dllexport' attribute

diff -u ./src/resources.c~ ./src/resources.c
--- ./src/resources.c~	2011-03-05 14:45:35.000000000 +0100
+++ ./src/resources.c	2011-05-11 09:56:10.983500000 +0200
@@ -61,7 +61,7 @@
 	COND_DESTROY(&counter.condvar);
 }
 
-static XS(end_locker) {
+XS(end_locker) {
 	dVAR; dXSARGS;
 	perl_mutex* mutex;