[DOC] Asciidoc rendering issue in `design-guide/borland.html`.

# [DOC] Asciidoc rendering issue in `design-guide/borland.html`.

## Link:
https://www.boost.org/doc/contributor-guide/design-guide/borland.html
## Issue:
The following snippet:
```cpp
f(static_cast(h)); // should work (std:13.4-1.6 with 5.2.9)
```
Is not valid ISO C++, it is probably an Asciidoc issue here.

## Full snippet:

```cpp
template
void f( void(\*g)(Arg) );

void h(int);
void h(double);

template
void h2(T);

int main()
{
void (\*p)(int) = h; // this works (std:13.4-1.1)
void (\*p2)(unsigned char) = h2; // this works as well (std:13.4-1.1)
f(h2); // this also works (std:13.4-1.3)

// "Cannot generate template specialization from h(int)",
// "Could not find a match for f(void (\*)(int))"
f(h); // should work (std:13.4-1.3)

f( (void(\*)(double))h); // C-style cast works (std:13.4-1.6 with 5.4)

// "Overloaded 'h' ambiguous in this context"
f(static_cast(h)); // should work (std:13.4-1.6 with 5.2.9)
}
```