Add compile-time errors for unsupported systems.
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index c9f6957..6f6fde4 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -31,11 +31,13 @@
#if defined(__ultrix) && defined(__mips) && defined(_DECTHREADS_)
/* _DECTHREADS_ is defined in cma.h which is included by pthread.h */
# define PY_PTHREAD_D4
+# error Systems with PY_PTHREAD_D4 are unsupported. See README.
#elif defined(__osf__) && defined (__alpha)
/* _DECTHREADS_ is defined in cma.h which is included by pthread.h */
# if !defined(_PTHREAD_ENV_ALPHA) || defined(_PTHREAD_USE_D4) || defined(PTHREAD_USE_D4)
# define PY_PTHREAD_D4
+# error Systems with PY_PTHREAD_D4 are unsupported. See README.
# else
# define PY_PTHREAD_STD
# endif
@@ -50,13 +52,16 @@
# define PY_PTHREAD_STD
# else
# define PY_PTHREAD_D7
+# error Systems with PY_PTHREAD_D7 are unsupported. See README.
# endif
#elif defined(__DGUX)
# define PY_PTHREAD_D6
+# error Systems with PY_PTHREAD_D6 are unsupported. See README.
#elif defined(__hpux) && defined(_DECTHREADS_)
# define PY_PTHREAD_D4
+# error Systems with PY_PTHREAD_D4 are unsupported. See README.
#else /* Default case */
# define PY_PTHREAD_STD