x/sys: add unsafe mmap, munmap, mremap

Fixes golang/go#56123

Author: ncruces

Diff for: unix/mremap.go

@@ -50,3 +50,8 @@ func (m *mremapMmapper) Mremap(oldData []byte, newLength int, flags int) (data [
 func Mremap(oldData []byte, newLength int, flags int) (data []byte, err error) {
 	return mapper.Mremap(oldData, newLength, flags)
 }
+
+func MremapPtr(oldAddr unsafe.Pointer, oldSize uintptr, newAddr unsafe.Pointer, newSize uintptr, flags int) (ret unsafe.Pointer, err error) {
+	xaddr, err := mapper.mremap(uintptr(oldAddr), oldSize, newSize, flags, uintptr(newAddr))
+	return unsafe.Pointer(xaddr), err
+}

Diff for: unix/syscall_unix.go

@@ -154,6 +154,15 @@ func Munmap(b []byte) (err error) {
 	return mapper.Munmap(b)
 }
 
+func MmapPtr(addr unsafe.Pointer, length uintptr, prot int, flags int, fd int, offset int64) (ret unsafe.Pointer, err error) {
+	xaddr, err := mapper.mmap(uintptr(addr), length, prot, flags, fd, offset)
+	return unsafe.Pointer(xaddr), err
+}
+
+func MunmapPtr(addr unsafe.Pointer, length uintptr) (err error) {
+	return mapper.munmap(uintptr(addr), length)
+}
+
 func Read(fd int, p []byte) (n int, err error) {
 	n, err = read(fd, p)
 	if raceenabled {