Hook up ARM architecture flags to GN build.

build/config/arm.gni

Index: build/config/arm.gni
diff --git a/build/config/arm.gni b/build/config/arm.gni
index 1feec385aae60c853b2c01f3a388b706d45e1090..ead3cf77773783b9840236ed0e2e3836b8918031 100644
--- a/build/config/arm.gni
+++ b/build/config/arm.gni
@@ -7,3 +7,35 @@ declare_args() {
   # platforms.
   arm_version = 7
 }
+
+if (is_android) {
+  arm_use_neon = false
+  # Our version of arm_neon_optional from common.gypi. This is not used in the
+  # current build so is commented out for now.
+  #arm_optionally_use_neon = false
+} else {
+  arm_use_neon = true
+  #arm_optionally_use_neon = true
+}
+
+if (arm_version == 6) {
+  arm_arch = "armv6"
+  arm_tune = ""
+  arm_float_abi = "softfp"
+  arm_fpu = "vfp"
+  # Thumb is a reduced instruction set available on some ARM processors that
+  # has increased code density.
+  arm_use_thumb = false
+
+} else if (arm_version == 7) {
+  arm_arch = "armv7-a"
+  arm_tune = "cortex-a8"
+  arm_float_abi = "softfp"
+  arm_use_thumb = true
+
+  if (arm_use_neon) {
+    arm_fpu = "neon"
+  } else {
+    arm_fpu = "vfpv3-d16"
+  }
+}