defined mode preprocessors

- ENABLE_DISTRIBUTION
- ENABLE_MULTITHREADING
- ENABLE_DISTRIBUTION

These names reflect that the compile-time processors _enable_ the corresponding modes but do not enforce required use; deployment can still be chosen at runtime / Qureg instantiation

quest/include/modes.h

@@ -7,4 +7,36 @@
 
 
 
+// ensure all mode flags are defined
+
+#ifndef ENABLE_DISTRIBUTION
+    #error "Compiler must define ENABLE_DISTRIBUTION"
+#endif
+
+#ifndef ENABLE_MULTITHREADING
+    #error "Compiler must define ENABLE_MULTITHREADING"
+#endif
+
+#ifndef ENABLE_GPU_ACCELERATION
+    #error "Compiler must define ENABLE_GPU_ACCELERATION"
+#endif
+
+
+
+// ensure all mode flags are valid values
+
+#if ! (ENABLE_DISTRIBUTION == 0 || ENABLE_DISTRIBUTION == 1)
+    #error "Macro ENABLE_DISTRIBUTION must have value 0 or 1"
+#endif
+
+#if ! (ENABLE_MULTITHREADING == 0 || ENABLE_MULTITHREADING == 1)
+    #error "Macro ENABLE_MULTITHREADING must have value 0 or 1"
+#endif
+
+#if ! (ENABLE_GPU_ACCELERATION == 0 || ENABLE_GPU_ACCELERATION == 1)
+    #error "Macro ENABLE_GPU_ACCELERATION must have value 0 or 1"
+#endif
+
+
+
 #endif // MODES_H