Added include of 'stddef.h' to 'unity_internals.h' if 'UNITY_EXCLUDE_STDDEF_H'...

Added include of 'stddef.h' to 'unity_internals.h' if 'UNITY_EXCLUDE_STDDEF_H' is not defined. This adds compiler independent support for the 'NULL' macro.

docs/UnityConfigurationGuide.md

@@ -215,6 +215,18 @@ Guide.
 _Example:_
         #define UNITY_FLOAT_PRECISION 0.001f
 
+### Miscellaneous
+
+##### `UNITY_EXCLUDE_STDDEF_H`
+
+Unity uses the `NULL` macro, which defines the value of a null pointer constant,
+defined in `stddef.h` by default. If you want to provide
+your own macro for this, you should exclude the `stddef.h` header file by adding this
+define to your configuration.
+
+_Example:_
+        #define UNITY_EXCLUDE_STDDEF_H
+
 
 ### Toolset Customization
 

src/unity_internals.h

@@ -19,6 +19,10 @@
 #include <math.h>
 #endif
 
+#ifndef UNITY_EXCLUDE_STDDEF_H
+#include <stddef.h>
+#endif
+
 /* Unity Attempts to Auto-Detect Integer Types
  * Attempt 1: UINT_MAX, ULONG_MAX in <limits.h>, or default to 32 bits
  * Attempt 2: UINTPTR_MAX in <stdint.h>, or default to same size as long