*sad4d_sse2.asm: fix 64-bit checks

use ARCH_X86_64 rather than UNIX64; fixes crashes on windows

Bug: aomedia:3273
Bug: aomedia:3176
Fixed: aomedia:3176
Change-Id: I8ffb56c888db026845f7c5372927f858cb0eb863
(cherry picked from commit 46011c642b335bede2a9fcd8bc1916edb09ccf2f)

aom_dsp/x86/highbd_sad4d_sse2.asm

diff --git a/aom_dsp/x86/highbd_sad4d_sse2.asm b/aom_dsp/x86/highbd_sad4d_sse2.asm
index 7ae1ca1..9442cd0 100644
--- a/aom_dsp/x86/highbd_sad4d_sse2.asm
+++ b/aom_dsp/x86/highbd_sad4d_sse2.asm
@@ -221,21 +221,21 @@
 ;   3: If 0, then normal sad, if 2, then skip every other row
 %macro HIGH_SADNXN4D 2-3 0
 %if %3 == 0  ; normal sad
-%if UNIX64
+%if ARCH_X86_64
 cglobal highbd_sad%1x%2x4d, 5, 8, 8, src, src_stride, ref1, ref_stride, \
                               res, ref2, ref3, ref4
 %else
 cglobal highbd_sad%1x%2x4d, 4, 7, 8, src, src_stride, ref1, ref_stride, \
                               ref2, ref3, ref4
-%endif  ; UNIX64
+%endif  ; ARCH_X86_64
 %else  ; %3 == 2, downsample
-%if UNIX64
+%if ARCH_X86_64
 cglobal highbd_sad_skip_%1x%2x4d, 5, 8, 8, src, src_stride, ref1, ref_stride, \
                               res, ref2, ref3, ref4
 %else
 cglobal highbd_sad_skip_%1x%2x4d, 4, 7, 8, src, src_stride, ref1, ref_stride, \
                               ref2, ref3, ref4
-%endif  ; UNIX64
+%endif  ; ARCH_X86_64
 %endif  ; sad/avg/skip
 
 ; set m1

aom_dsp/x86/sad4d_sse2.asm

diff --git a/aom_dsp/x86/sad4d_sse2.asm b/aom_dsp/x86/sad4d_sse2.asm
index 343a14d..fe2e6ad 100644
--- a/aom_dsp/x86/sad4d_sse2.asm
+++ b/aom_dsp/x86/sad4d_sse2.asm
@@ -319,7 +319,7 @@
 ;   4: If 0, then normal sad, else skip rows
 %macro SADNXN4D 2-4 0,0
 %if %4 == 1  ; skip rows
-%if UNIX64
+%if ARCH_X86_64
 cglobal sad_skip_%1x%2x4d, 5, 8, 8, src, src_stride, ref1, ref_stride, \
                               res, ref2, ref3, ref4
 %else
@@ -327,7 +327,7 @@
                               ref2, ref3, ref4
 %endif
 %elif %3 == 0  ; normal sad
-%if UNIX64
+%if ARCH_X86_64
 cglobal sad%1x%2x4d, 5, 8, 8, src, src_stride, ref1, ref_stride, \
                               res, ref2, ref3, ref4
 %else
@@ -335,7 +335,7 @@
                               ref2, ref3, ref4
 %endif
 %else ; avg
-%if UNIX64
+%if ARCH_X86_64
 cglobal sad%1x%2x4d_avg, 6, 10, 8, src, src_stride, ref1, ref_stride, \
                                   second_pred, res, ref2, ref3, ref4
 %else
@@ -346,7 +346,7 @@
 %endif
 %endif
 
-  %define mflag ((1 - UNIX64) & %3)
+  %define mflag ((1 - ARCH_X86_64) & %3)
 %if %4 == 1
   lea          src_strided, [2*src_strided]
   lea          ref_strided, [2*ref_strided]