cmd/dist: enable GOARM>5 on NetBSD/ARM.

Tested GOARM=6 on Raspberry Pi, and I found only a few tests that
use sub-normal numbers fails. I have a patch to NetBSD kernel pending
that fixes this issue (NetBSD kernel doesn't allow us to disable the
Flush-to-Zero feature).

LGTM=jsing
R=golang-codereviews, jsing
CC=golang-codereviews
https://golang.org/cl/70730043

src/cmd/dist/arm.c

@@ -17,16 +17,8 @@ static void useVFPv1(void);
 char *
 xgetgoarm(void)
 {
-#if defined(__NetBSD__) || defined(__FreeBSD__)
-	// NetBSD has buggy support for VFPv2 (incorrect inexact, 
-	// denormial, and NaN handling). When GOARM=6, some of our
-	// math tests fails on Raspberry Pi.
-	// Thus we return "5" here for safety, the user is free
-	// to override.
-	// Note: using GOARM=6 with cgo can trigger a kernel assertion
-	// failure and crash NetBSD/evbarm kernel.
-	// FreeBSD also have broken VFP support, so disable VFP also
-	// on FreeBSD.
+#if defined(__FreeBSD__)
+	// FreeBSD has broken VFP support
 	return "5";
 #endif
 	if(xtryexecfunc(useVFPv3))