API BREAKER: Replacing defines in irrTypes.h which are conflicting with c++ reserved identifier rules.

C++ has undefined behavior for identifiers starting with __ or with _ followed by an uppercase letter.
We still have many more (in IrrCompileConfig.h and in all header-guards), will likely replace those later as well.
As a workaround for users which might use irrlicht defines in their code, I've added the header irrLegacyDefines.h
Including that allows to continue using old defines for a while - or make it easier to have code which compiles 
with old and new Irrlicht library versions.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6251 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/irrXML.cpp

@@ -48,7 +48,7 @@ public:
 	}
 
 	//! Reads an amount of bytes from the file.
-	virtual int read(void* buffer, int sizeToRead) _IRR_OVERRIDE_
+	virtual int read(void* buffer, int sizeToRead) IRR_OVERRIDE
 	{
 		if (!File)
 			return 0;
@@ -57,7 +57,7 @@ public:
 	}
 
 	//! Returns size of file in bytes
-	virtual long getSize() const _IRR_OVERRIDE_
+	virtual long getSize() const IRR_OVERRIDE
 	{
 		return Size;
 	}