android+chromeos: Make sure 32-bit android arm builds use -mfloat-abi=softfp.

...even in Chrome OS builds that set `arm_float_abi = "hard"` for the
outer Chrome OS builds -- the inner android build (for arc) should still
use the regular Android softfloat abi.

Bug: 1144188
Change-Id: I3cf726ce4134ad4d8cce8def8647d5851c081a63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510772
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822841}

build/config/arm.gni

@@ -87,6 +87,12 @@ if (current_cpu == "arm" || v8_current_cpu == "arm") {
       } else {
         arm_float_abi = "hard"
       }
+    } else if (current_os == "android") {
+      # The build/toolchain/android:android_clang_arm toolchain explicitly
+      # enforces this, so that chromeos builds can customize arm_float_abi
+      # for the outer chromeos build without affecting the android portion of
+      # a chromeos build.
+      assert(arm_float_abi == "softfp")
     }
 
     if (arm_fpu == "") {

build/toolchain/android/BUILD.gn

@@ -96,6 +96,7 @@ android_clang_toolchain("android_clang_arm") {
   binary_prefix = "arm-linux-androideabi"
   toolchain_args = {
     current_cpu = "arm"
+    arm_float_abi = "softfp"
   }
 }