cpu: unexport HWCap and HWCap2

These are an implementation detail and should not have been
exported. This only affects Linux on platforms other than 386 and
amd64.

Fixes golang/go#30255.

Change-Id: Ib23b42a7309fd6093b6b9d8b6628de222a3928be
Reviewed-on: https://go-review.googlesource.com/c/163004
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

cpu/cpu_linux.go

@@ -22,8 +22,8 @@ const (
 // For those platforms don't have a 'cpuid' equivalent we use HWCAP/HWCAP2
 // These are initialized in cpu_$GOARCH.go
 // and should not be changed after they are initialized.
-var HWCap uint
-var HWCap2 uint
+var hwCap uint
+var hwCap2 uint
 
 func init() {
 	buf, err := ioutil.ReadFile(procAuxv)
@@ -46,9 +46,9 @@ func init() {
 		}
 		switch tag {
 		case _AT_HWCAP:
-			HWCap = val
+			hwCap = val
 		case _AT_HWCAP2:
-			HWCap2 = val
+			hwCap2 = val
 		}
 	}
 	doinit()