Fix _SFR_IO8 macro definition -- use volatile keyword to prevent optimization

Author: ianfixes

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 - Don't define `ostream& operator<<(nullptr_t)` if already defined by Apple
 - `CppLibrary.in_tests_dir?` no longer produces an error if there is no tests directory
+- The definition of the `_SFR_IO8` macro no longer produces errors about rvalues
 
 ### Deprecated
 - `arduino_ci_remote.rb` CLI switch `--skip-compilation`

SampleProjects/TestSomething/test/defines.cpp

@@ -8,4 +8,15 @@ unittest(binary)
   assertEqual(100, B1100100);
 }
 
+#define DDRE      _SFR_IO8(0x02)
+
+unittest(SFR_IO8)
+{
+  // in normal arduino code, you can do this.  in arduino_ci, you might get an
+  // error like: cannot take the address of an rvalue of type 'int'
+  //
+  // this tests that directly
+  &DDRE;
+}
+
 unittest_main()

cpp/arduino/avr/io.h

@@ -96,7 +96,7 @@
 #ifndef _AVR_IO_H_
 #define _AVR_IO_H_
 
-#define _SFR_IO8(io_addr) (io_addr) // this macro is all we need from the sfr file
+#define _SFR_IO8(io_addr) (*(volatile uint8_t *)(io_addr)) // this macro is all we need from the sfr file
 
 #if defined (__AVR_AT94K__)
 #  include "ioat94k.h"