Add a [rtc_]build_with_neon variable to unify conditions.

webrtc/modules/audio_processing/BUILD.gn

Index: webrtc/modules/audio_processing/BUILD.gn
diff --git a/webrtc/modules/audio_processing/BUILD.gn b/webrtc/modules/audio_processing/BUILD.gn
index 092be1ef14356c5b61170b8f20ac743cb16eee20..788334fb7b6b3b2a433973f5151df85ddd528a28 100644
--- a/webrtc/modules/audio_processing/BUILD.gn
+++ b/webrtc/modules/audio_processing/BUILD.gn
@@ -176,7 +176,7 @@ source_set("audio_processing") {
     deps += [ ":audio_processing_sse2" ]
   }
 
-  if (rtc_build_armv7_neon || current_cpu == "arm64") {
+  if (rtc_build_with_neon) {
     deps += [ ":audio_processing_neon" ]
   }
 
@@ -238,7 +238,7 @@ if (current_cpu == "x86" || current_cpu == "x64") {
   }
 }
 
-if (rtc_build_armv7_neon || current_cpu == "arm64") {
+if (rtc_build_with_neon) {
   source_set("audio_processing_neon") {
     sources = [
       "aec/aec_core_neon.c",
@@ -247,32 +247,14 @@ if (rtc_build_armv7_neon || current_cpu == "arm64") {
       "ns/nsx_core_neon.c",
     ]
 
-    configs += [ "../..:common_config" ]
+    configs += [
+      "../..:arm_neon_config",
+      "../..:common_config",
+    ]
     public_configs = [ "../..:common_inherited_config" ]
 
     deps = [
       "../../common_audio",
     ]
-
-    # 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" ]
-
-    # "-mfpu=neon" is not requried for arm64 in GCC.
-    if (current_cpu != "arm64") {
-      cflags = [ "-mfpu=neon" ]
-    }
-
-    # Disable LTO in audio_processing_neon target due to compiler bug.
-    if (rtc_use_lto) {
-      cflags -= [
-        "-flto",
-        "-ffat-lto-objects",
-      ]
-    }
   }
 }