Fix tracing in libts

Libts deployments did not include posix_trace.c in the build and as
a result setting TRACE_LEVEL to any value above TRACE_LEVEL_NONE
resulted in a build error.

- Add the missing C file to the build to fix this error.
- Make the arm-linux version of libts to implement tracing
the same way as linux-pc.

Change-Id: I1db6117a0e8aa4955de063e7b22618d4a254973f
Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
diff --git a/components/common/trace/include/trace.h b/components/common/trace/include/trace.h
index d9b6c07..4395e41 100644
--- a/components/common/trace/include/trace.h
+++ b/components/common/trace/include/trace.h
@@ -8,6 +8,12 @@
 
 #include "compiler.h"
 
+#ifdef EXPORT_PUBLIC_INTERFACE_TRACE
+#define TRACE_EXPORTED __attribute__((__visibility__("default")))
+#else
+#define TRACE_EXPORTED
+#endif
+
 #define TRACE_LEVEL_NONE	(0)
 #define TRACE_LEVEL_ERROR	(1)
 #define TRACE_LEVEL_INFO	(2)
@@ -30,6 +36,7 @@
 
 extern void (*trace_puts_interface)(const char *str);
 void trace_puts(const char *str);
+TRACE_EXPORTED
 void trace_printf(const char *func, int line, int level, const char *fmt, ...) __printf(4, 5);
 
 #if TRACE_LEVEL >= TRACE_LEVEL_ERROR