Add a [rtc_]build_with_neon variable to unify conditions.

webrtc/common_audio/common_audio.gyp

Index: webrtc/common_audio/common_audio.gyp
diff --git a/webrtc/common_audio/common_audio.gyp b/webrtc/common_audio/common_audio.gyp
index 36e6a65ebd086d5cfca542df3344d72e3add683b..884a8afcf84a7924eabe5320f959fa79e9c7d607 100644
--- a/webrtc/common_audio/common_audio.gyp
+++ b/webrtc/common_audio/common_audio.gyp
@@ -136,6 +136,9 @@
         ['target_arch=="ia32" or target_arch=="x64"', {
           'dependencies': ['common_audio_sse2',],
         }],
+        ['build_with_neon==1', {
+          'dependencies': ['common_audio_neon',],
+        }],
         ['target_arch=="arm"', {
           'sources': [
             'signal_processing/complex_bit_reverse_arm.S',
@@ -147,7 +150,6 @@
           ],
           'conditions': [
             ['arm_version>=7', {
-              'dependencies': ['common_audio_neon',],
               'sources': [
                 'signal_processing/filter_ar_fast_q12_armv7.S',
               ],
@@ -157,9 +159,6 @@
             }],
           ],  # conditions
         }],
-        ['target_arch=="arm64"', {
-          'dependencies': ['common_audio_neon',],
-        }],
         ['target_arch=="mipsel" and mips_arch_variant!="r6"', {
           'sources': [
             'signal_processing/include/spl_inl_mips.h',
@@ -212,7 +211,7 @@
         },
       ],  # targets
     }],
-    ['target_arch=="arm" and arm_version>=7 or target_arch=="arm64"', {
+    ['build_with_neon==1', {
       'targets': [
         {
           'target_name': 'common_audio_neon',
@@ -225,15 +224,6 @@
             'signal_processing/downsample_fast_neon.c',
             'signal_processing/min_max_operations_neon.c',
           ],
-          'conditions': [
-            # Disable LTO in common_audio_neon target due to compiler bug
-            ['use_lto==1', {
-              'cflags!': [
-                '-flto',
-                '-ffat-lto-objects',
-              ],
-            }],
-          ],
         },
       ],  # targets
     }],