x86inc: Avoid creating unnecessary local labels

The REP_RET workaround is only needed on old AMD cpus, and the labels clutter
up the symbol table and confuse debugging/profiling tools, so use EQU to
create SHN_ABS symbols instead of creating local labels. Furthermore, skip
the workaround completely in functions that definitely won't run on such cpus.

Note that EQU is just creating a local label when using nasm instead of yasm.
This is probably a bug, but at least it doesn't break anything.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavutil/x86/x86inc.asm

@@ -648,8 +648,10 @@ DECLARE_ARG 7, 8, 9, 10, 11, 12, 13, 14
     %rep %0
         %macro %1 1-2 %1
             %2 %1
-            %%branch_instr:
+            %if notcpuflag(ssse3)
+                %%branch_instr equ $
                 %xdefine last_branch_adr %%branch_instr
+            %endif
         %endmacro
         %rotate 1
     %endrep