Fix config.m4 --enable-apcu-{rwlocks,mmap}

## --**enable**-apcu-{rwlocks,mmap} _disables_ feature

This patch fixes those cases, enabling mmap and rwlocks by default.

### Before:

```sh
# rwlocks
$ ./configure | grep rwlocks
checking if APCu should be allowed to use rwlocks... yes
configure: WARNING: APCu has access to native rwlocks

$ ./configure --enable-apcu-rwlocks | grep rwlocks
checking if APCu should be allowed to use rwlocks... no
configure: WARNING: APCu has access to mutexes

$ ./configure --disable-apcu-rwlocks | grep rwlocks
checking if APCu should be allowed to use rwlocks... no
configure: WARNING: APCu has access to mutexes

# mmap
$ ./configure | grep mmap
checking if APCu will use mmap or shm... mmap

$ ./configure --enable-apcu-mmap | grep mmap
checking if APCu will use mmap or shm... shm

$ ./configure --disable-apcu-mmap | grep mmap
checking if APCu will use mmap or shm... shm
```

### After:

```sh
# rwlocks
$ ./configure | grep rwlocks
checking if APCu should be allowed to use rwlocks... yes
configure: WARNING: APCu has access to native rwlocks

./configure --enable-apcu-rwlocks | grep rwlocks
checking if APCu should be allowed to use rwlocks... yes
configure: WARNING: APCu has access to native rwlocks

$ ./configure --disable-apcu-rwlocks | grep rwlocks
checking if APCu should be allowed to use rwlocks... no
configure: WARNING: APCu has access to mutexes

# mmap
$ ./configure | grep mmap
checking if APCu will use mmap or shm... mmap

$ ./configure --enable-apcu-mmap | grep mmap
checking if APCu will use mmap or shm... mmap

$ ./configure --disable-apcu-mmap | grep mmap
checking if APCu will use mmap or shm... shm
```