Set proper ELF attributes for the ARM assembly functions

Fixes linking related fragility, which could result in crashes
when doing Thumb2->ARM function calls.
Reported-by: Luc Verhaegen <libv@skynet.be>
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

src/arm_asm.S

@@ -41,6 +41,10 @@
 
 .macro asm_function function_name
     .global \function_name
+#ifdef __ELF__
+    .hidden \function_name
+    .type \function_name, %function
+#endif
 .func \function_name
 \function_name:
 .endm