tests/tcg/multiarch: add hello world system test

This is not really i386 only, we can have the same test for all
architectures supporting system tests.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

tests/tcg/multiarch/system/hello.c

@@ -0,0 +1,14 @@
+/*
+ * Hello World, system test version
+ *
+ * We don't have the benefit of libc, just builtin C primitives and
+ * whatever is in minilib.
+ */
+
+#include <minilib.h>
+
+int main(void)
+{
+    ml_printf("Hello World\n");
+    return 0;
+}