null pointer dereference detection in DMD

[Richard (Rikki) Andrew Cattermole]

For clang:

flags: ``-Wall --analyze``

```
<source>:5:10: warning: Dereference of null pointer (loaded from 
variable 'ptr') [core.NullDereference]
     5 |     *ptr = 3;
       |      ~~~ ^
1 warning generated.
ASM generation compiler returned: 0
clang: warning: -Wl,-rpath,./lib: 'linker' input unused 
[-Wunused-command-line-argument]
clang: warning: -Wl,-rpath,/opt/compiler-explorer/gcc-13.2.0/lib64: 
'linker' input unused [-Wunused-command-line-argument]
clang: warning: -Wl,-rpath,/opt/compiler-explorer/gcc-13.2.0/lib32: 
'linker' input unused [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-L./lib' 
[-Wunused-command-line-argument]
<source>:5:10: warning: Dereference of null pointer (loaded from 
variable 'ptr') [core.NullDereference]
     5 |     *ptr = 3;
       |      ~~~ ^
1 warning generated.
Execution build compiler returned: 0
Program returned: 255
```