[feature] Display address-model and architecture

Feature request: display the address-model and architecture which are being used in the build.

Problem description:

Here is an example of running b2 with the address-model set to 32-bit.

```
../../b2 -a -j8 bench link=static variant=release address-model=32 toolset=clang
Performing configuration checks

- default address-model : 64-bit
- default architecture : x86
- symlinks supported : yes
...patience...
...found 1616 targets...
...updating 36 targets...
```

The user may wonder "did it catch that address-model flag? It appears to be building 64-bit, even though 32-bit was configured."

Possible Solution 1:

Display the latest accurate info without the word "default". Example:

```
../../b2 -a -j8 bench link=static variant=release address-model=32 toolset=clang
Performing configuration checks

- address-model : 32-bit
- architecture : x86
- symlinks supported : yes
...patience...
...found 1616 targets...
...updating 36 targets...
```

Possible Solution 2:

Show either the word "default" or "configured", depending on which one applies.

Example 2a:

```
../../b2 -a -j8 bench link=static variant=release toolset=clang
Performing configuration checks

- default address-model : 64-bit
- default architecture : x86
- symlinks supported : yes
...patience...
...found 1616 targets...
...updating 36 targets...
```

Example 2b:

```
../../b2 -a -j8 bench link=static variant=release address-model=32 toolset=clang
Performing configuration checks

- configured address-model : 32-bit
- default architecture : x86
- symlinks supported : yes
...patience...
...found 1616 targets...
...updating 36 targets...
```

Start by locating the B2 configuration-check code that produces the address-model and architecture lines shown in the issue. Trace how command-line settings are distinguished from defaults, then verify that runs with and without address-model=32 report the intended labels and values.

Written by the indexing model from the issue text.