AARCH64:fix variable name collision with register name

The variable name is g which is collision with the reserved name
for R28. This leads to bazel build failure on ARM with following
information:
(register+register) not supported on this architecture

rename it from g to ptr (referenced from golang source
code)

Signed-off-by: Howard Zhang <howard.zhang@arm.com>

pkg/syncevent/waiter_amd64.s

@@ -16,9 +16,9 @@
 
 // See waiter_noasm_unsafe.go for a description of waiterUnlock.
 //
-// func waiterUnlock(g unsafe.Pointer, wg *unsafe.Pointer) bool
+// func waiterUnlock(ptr unsafe.Pointer, wg *unsafe.Pointer) bool
 TEXT ·waiterUnlock(SB),NOSPLIT,$0-24
-	MOVQ g+0(FP), DI
+	MOVQ ptr+0(FP), DI
 	MOVQ wg+8(FP), SI
 
 	MOVQ $·preparingG(SB), AX

pkg/syncevent/waiter_arm64.s

@@ -16,11 +16,11 @@
 
 // See waiter_noasm_unsafe.go for a description of waiterUnlock.
 //
-// func waiterUnlock(g unsafe.Pointer, wg *unsafe.Pointer) bool
+// func waiterUnlock(ptr unsafe.Pointer, wg *unsafe.Pointer) bool
 TEXT ·waiterUnlock(SB),NOSPLIT,$0-24
 	MOVD wg+8(FP), R0
 	MOVD $·preparingG(SB), R1
-	MOVD g+0(FP), R2
+	MOVD ptr+0(FP), R2
 again:
 	LDAXR (R0), R3
 	CMP R1, R3

pkg/syncevent/waiter_asm_unsafe.go

@@ -21,4 +21,4 @@ import (
 )
 
 // See waiter_noasm_unsafe.go for a description of waiterUnlock.
-func waiterUnlock(g unsafe.Pointer, wg *unsafe.Pointer) bool
+func waiterUnlock(ptr unsafe.Pointer, wg *unsafe.Pointer) bool

pkg/syncevent/waiter_noasm_unsafe.go

@@ -32,8 +32,8 @@ import (
 // should be aborted.
 //
 //go:nosplit
-func waiterUnlock(g unsafe.Pointer, wg *unsafe.Pointer) bool {
+func waiterUnlock(ptr unsafe.Pointer, wg *unsafe.Pointer) bool {
 	// The only way this CAS can fail is if a call to Waiter.NotifyPending()
 	// has replaced *wg with nil, in which case we should not sleep.
-	return atomic.CompareAndSwapPointer(wg, (unsafe.Pointer)(&preparingG), g)
+	return atomic.CompareAndSwapPointer(wg, (unsafe.Pointer)(&preparingG), ptr)
 }