http://forum.canardpc.com/threads/110951-fix-build-with-newer-gcc-versions

the meaning of extern inline changed between standards.  use static inline
for these tiny I/O functions everywhere to keep things simple.

--- a/io.h
+++ b/io.h
@@ -31,6 +31,6 @@
  */
 
 #define __OUT1(s,x) \
-extern inline void __out##s(unsigned x value, unsigned short port) {
+static inline void __out##s(unsigned x value, unsigned short port) {
 
 #define __OUT2(s,s1,s2) \
@@ -43,6 +43,6 @@
 __OUT1(s##c_p,x) __OUT2(s,s1,"") : : "a" (value), "id" (port)); SLOW_DOWN_IO; }
 
 #define __IN1(s) \
-extern inline RETURN_TYPE __in##s(unsigned short port) { RETURN_TYPE _v;
+static inline RETURN_TYPE __in##s(unsigned short port) { RETURN_TYPE _v;
 
 #define __IN2(s,s1,s2) \
@@ -55,6 +55,6 @@
 __IN1(s##c_p) __IN2(s,s1,"") : "=a" (_v) : "id" (port) ,##i ); SLOW_DOWN_IO; return _v; }
 
 #define __OUTS(s) \
-extern inline void outs##s(unsigned short port, const void * addr, unsigned long count) \
+static inline void outs##s(unsigned short port, const void * addr, unsigned long count) \
 { __asm__ __volatile__ ("cld ; rep ; outs" #s \
 : "=S" (addr), "=c" (count) : "d" (port),"0" (addr),"1" (count)); }