fix ldc2 compilation for Haiku; thanks to MrSunshine

dmd2/root/port.c

@@ -415,7 +415,9 @@ int Port::isFinite(double r)
     return ::finite(r);
 }
 
+#if !defined __HAIKU__
 #undef isinf
+#endif
 int Port::isInfinity(double r)
 {
 #if __APPLE__

dmd2/statement.c

@@ -29,6 +29,7 @@
 #include "template.h"
 #include "attrib.h"
 
+#include <pthread.h>
 #if IN_LLVM
 // sizes based on those from tollvm.cpp:DtoMutexType()
 int os_critsecsize()