all: use &^ operator if possible

This is a change improving consistency in the source tree.
The pattern foo &= ^bar, was only used six times in src/ directory.
The usage of the supported &^ (bit clear / AND NOT) operator is way more
common, about factor 10x.

Change-Id: If26a2994fd81d23d42189bee00245eb84e672cf3
Reviewed-on: https://go-review.googlesource.com/21224Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/gc/gsubr.go

@@ -244,7 +244,7 @@ func ggloblLSym(s *obj.LSym, width int32, flags int16) {
 	p.From.Sym = s
 	if flags&obj.LOCAL != 0 {
 		p.From.Sym.Local = true
-		flags &= ^obj.LOCAL
+		flags &^= obj.LOCAL
 	}
 	p.To.Type = obj.TYPE_CONST
 	p.To.Offset = int64(width)

src/cmd/link/internal/ld/link.go

@@ -129,7 +129,7 @@ func (a *Attribute) Set(flag Attribute, value bool) {
 	if value {
 		*a |= flag
 	} else {
-		*a &= ^flag
+		*a &^= flag
 	}
 }
 

src/crypto/elliptic/p256.go

@@ -1056,7 +1056,7 @@ func p256ScalarBaseMult(xOut, yOut, zOut *[p256Limbs]uint32, scalar *[32]uint8)
 			p256CopyConditional(yOut, &ty, mask)
 			p256CopyConditional(zOut, &tz, mask)
 			// If p was not zero, then n is now non-zero.
-			nIsInfinityMask &= ^pIsNoninfiniteMask
+			nIsInfinityMask &^= pIsNoninfiniteMask
 		}
 	}
 }
@@ -1136,7 +1136,7 @@ func p256ScalarMult(xOut, yOut, zOut, x, y *[p256Limbs]uint32, scalar *[32]uint8
 		p256CopyConditional(xOut, &tx, mask)
 		p256CopyConditional(yOut, &ty, mask)
 		p256CopyConditional(zOut, &tz, mask)
-		nIsInfinityMask &= ^pIsNoninfiniteMask
+		nIsInfinityMask &^= pIsNoninfiniteMask
 	}
 }
 

src/syscall/exec_unix.go

@@ -103,7 +103,7 @@ func SetNonblock(fd int, nonblocking bool) (err error) {
 	if nonblocking {
 		flag |= O_NONBLOCK
 	} else {
-		flag &= ^O_NONBLOCK
+		flag &^= O_NONBLOCK
 	}
 	_, err = fcntl(fd, F_SETFL, flag)
 	return err

src/syscall/lsf_linux.go

@@ -56,7 +56,7 @@ func SetLsfPromisc(name string, m bool) error {
 	if m {
 		ifl.flags |= uint16(IFF_PROMISC)
 	} else {
-		ifl.flags &= ^uint16(IFF_PROMISC)
+		ifl.flags &^= uint16(IFF_PROMISC)
 	}
 	_, _, ep = Syscall(SYS_IOCTL, uintptr(s), SIOCSIFFLAGS, uintptr(unsafe.Pointer(&ifl)))
 	if ep != 0 {