Avoid 'amdnop' when building with nasm

Other implementations of x86inc.asm have more comprehensive nasm
workarounds. This is the only thing that was changed for the previous
import to libvpx. See if we can still get away with it.

Change-Id: I3ef6fe9a4816461c89431a82b7e4a08b4b948d39

third_party/x86inc/README.libvpx

diff --git a/third_party/x86inc/README.libvpx b/third_party/x86inc/README.libvpx
index 629cece..13d86ad 100644
--- a/third_party/x86inc/README.libvpx
+++ b/third_party/x86inc/README.libvpx
@@ -14,3 +14,4 @@
   exist in libvpx.
 Expand PIC default to macho64 and respect CONFIG_PIC from libvpx
 Catch all elf formats for 'hidden' status and SECTION notes.
+Avoid 'amdnop' when building with nasm.

third_party/x86inc/x86inc.asm.new

diff --git a/third_party/x86inc/x86inc.asm.new b/third_party/x86inc/x86inc.asm.new
index b38ae9e..c516a78 100644
--- a/third_party/x86inc/x86inc.asm.new
+++ b/third_party/x86inc/x86inc.asm.new
@@ -806,7 +806,10 @@
         %endif
     %endif
 
-    %if ARCH_X86_64 || cpuflag(sse2)
+    %ifdef __NASM_VER__
+        %use smartalign
+        ALIGNMODE k7
+    %elif ARCH_X86_64 || cpuflag(sse2)
         CPU amdnop
     %else
         CPU basicnop