arm: LLVMLinux: use static inline in ARM ftrace.h

With compilers which follow the C99 standard (like modern versions of gcc and
clang), "extern inline" does the wrong thing (emits code for an externally
linkable version of the inline function). In this case using static inline
and removing the NULL version of return_address in return_address.c does
the right thing.
Signed-off-by: Behan Webster <behanw@converseincode.com>
Reviewed-by: Mark Charlebois <charlebm@gmail.com>

source: http://www.serverphorums.com/read.php?12,880351,880351#msg-880351

arch/arm/include/asm/ftrace.h

@@ -45,7 +45,7 @@ void *return_address(unsigned int);
 
 #else
 
-extern inline void *return_address(unsigned int level)
+static inline void *return_address(unsigned int level)
 {
 	return NULL;
 }

arch/arm/kernel/return_address.c

@@ -62,10 +62,12 @@ void *return_address(unsigned int level)
 #warning "TODO: return_address should use unwind tables"
 #endif
 
+/*
 void *return_address(unsigned int level)
 {
 	return NULL;
 }
+*/
 
 #endif /* if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND) / else */