Revert 8632 "Enable isac NEON building on Aarch64"

Breaks Chromium audio tests on Nexus 9.
http://build.chromium.org/p/chromium.webrtc.fyi/builders/Android%20Tests%20%28dbg%29%20%28L%20Nexus9%29/builds/1152/steps/content_browsertests/logs/stdio

It also actually broke already on our android_arm64 trybot in the CL:
http://build.chromium.org/p/tryserver.webrtc/builders/android_arm64/builds/3282
but I failed to double-check that (I guess I assumed it was flakiness since
that bot has been flaking a lot lately).

> Enable isac NEON building on Aarch64
> 
> Passed building isac_neon and modules_unittests on Android ARM64 and ARMv7.
> Passed modules_unittests with following filters:
>   --gtest_filter=FiltersTest*
>   --gtest_filter=LpcMaskingModelTest*
>   --gtest_filter=TransformTest*
>   --gtest_filter=FilterBanksTest*
> 
> WebRtcIsacfix_CalculateResidualEnergyNeon is not enabled due to Issue 4224.
> 
> BUG=4002
> R=andrew@webrtc.org, jridges@masque.com, kjellander@webrtc.org
> 
> Review URL: https://webrtc-codereview.appspot.com/39979004
> 
> Patch from Zhongwei Yao <zhongwei.yao@arm.com>.

TBR=zhongwei.yao@arm.com, andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45559004

Cr-Commit-Position: refs/heads/master@{#8649}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8649 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/modules/audio_coding/BUILD.gn b/webrtc/modules/audio_coding/BUILD.gn
index 0832d6f..6e280da 100644
--- a/webrtc/modules/audio_coding/BUILD.gn
+++ b/webrtc/modules/audio_coding/BUILD.gn
@@ -532,10 +532,6 @@
     "../../system_wrappers",
   ]
 
-  if (cpu_arch == "arm64") {
-    deps += [ ":isac_neon" ]
-  }
-
   if (rtc_build_armv7_neon) {
     deps += [ ":isac_neon" ]
 
@@ -586,39 +582,16 @@
   }
 }
 
-if (rtc_build_armv7_neon || cpu_arch == "arm64") {
+if (rtc_build_armv7_neon) {
   source_set("isac_neon") {
-    sources = [ "codecs/isac/fix/source/entropy_coding_neon.c" ]
-
-    if (rtc_build_armv7_neon) {
-      sources += [
-        "codecs/isac/fix/source/filterbanks_neon.S",
-        "codecs/isac/fix/source/filters_neon.S",
-        "codecs/isac/fix/source/lattice_neon.S",
-        "codecs/isac/fix/source/lpc_masking_model_neon.S",
-        "codecs/isac/fix/source/transform_neon.S",
-      ]
-
-      # Enable compilation for the ARM v7 Neon instruction set. This is needed
-      # since //build/config/arm.gni only enables Neon for iOS, not Android.
-      # This provides the same functionality as webrtc/build/arm_neon.gypi.
-      # TODO(kjellander): Investigate if this can be moved into webrtc.gni or
-      # //build/config/arm.gni instead, to reduce code duplication.
-      # Remove the -mfpu=vfpv3-d16 cflag.
-      configs -= [ "//build/config/compiler:compiler_arm_fpu" ]
-      cflags = [
-        "-mfpu=neon",
-      ]
-    }
-
-    if (cpu_arch == "arm64") {
-      sources += [
-        "codecs/isac/fix/source/filterbanks_neon.c",
-        "codecs/isac/fix/source/filters_neon.c",
-        "codecs/isac/fix/source/lattice_neon.c",
-        "codecs/isac/fix/source/transform_neon.c",
-      ]
-    }
+    sources = [
+      "codecs/isac/fix/source/entropy_coding_neon.c",
+      "codecs/isac/fix/source/filterbanks_neon.S",
+      "codecs/isac/fix/source/filters_neon.S",
+      "codecs/isac/fix/source/lattice_neon.S",
+      "codecs/isac/fix/source/lpc_masking_model_neon.S",
+      "codecs/isac/fix/source/transform_neon.S",
+    ]
 
     include_dirs = [
       "../../..",
@@ -632,6 +605,17 @@
       ]
     }
 
+    # Enable compilation for the ARM v7 Neon instruction set. This is needed
+    # since //build/config/arm.gni only enables Neon for iOS, not Android.
+    # This provides the same functionality as webrtc/build/arm_neon.gypi.
+    # TODO(kjellander): Investigate if this can be moved into webrtc.gni or
+    # //build/config/arm.gni instead, to reduce code duplication.
+    # Remove the -mfpu=vfpv3-d16 cflag.
+    configs -= [ "//build/config/compiler:compiler_arm_fpu" ]
+    cflags = [
+      "-mfpu=neon",
+    ]
+
     configs += [ "../..:common_config" ]
     public_configs = [ "../..:common_inherited_config" ]