runtime: skip floating point hardware check on Android

CL 33652 removed the fake auxv for Android, and replaced it with
a /proc/self/auxv fallback. When /proc/self/auxv is unreadable,
however, hardware capabilities detection won't work and the runtime
will mistakenly think that floating point hardware is unavailable.

Fix this by always assuming floating point hardware on Android.

Manually tested on a Nexus 5 running Android 6.0.1. I suspect the
android/arm builder has a readable /proc/self/auxv and therefore
does not trigger the failure mode.

Change-Id: I95c3873803f9e17333c6cb8b9ff2016723104085
Reviewed-on: https://go-review.googlesource.com/34641Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/os_linux_arm.go

@@ -18,6 +18,12 @@ var armArch uint8 = 6 // we default to ARMv6
 var hwcap uint32      // set by setup_auxv
 
 func checkgoarm() {
+	// On Android, /proc/self/auxv might be unreadable and hwcap won't
+	// reflect the CPU capabilities. Assume that every Android arm device
+	// has the necessary floating point hardware available.
+	if GOOS == "android" {
+		return
+	}
 	if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
 		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
 		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")