Fix compilation with YASM.

YASM does not support %ifempty even though it is in the official
NASM documentation and supported since NASM 2.02.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavutil/x86/x86inc.asm

@@ -469,14 +469,14 @@ DECLARE_REG 6, ebp, ebp, bp, null, [esp + stack_offset + 28]
 %macro cglobal 1-2+ ; name, [PROLOGUE args]
 %if %0 == 1
     ; HACK: work around %+ broken with empty SUFFIX for nasm 2.09.10
-    %ifempty SUFFIX
+    %ifndef cpuname
     cglobal_internal %1
     %else
     cglobal_internal %1 %+ SUFFIX
     %endif
 %else
     ; HACK: work around %+ broken with empty SUFFIX for nasm 2.09.10
-    %ifempty SUFFIX
+    %ifndef cpuname
     cglobal_internal %1, %2
     %else
     cglobal_internal %1 %+ SUFFIX, %2
@@ -758,7 +758,7 @@ INIT_XMM
 ; Append cpuflags to the callee's name iff the appended name is known and the plain name isn't
 %macro call 1
     ; HACK: work around %+ broken with empty SUFFIX for nasm 2.09.10
-    %ifempty SUFFIX
+    %ifndef cpuname
     call_internal %1, %1
     %else
     call_internal %1, %1 %+ SUFFIX