freebsd dub linker error

[Alain De Vos]

Performed additional tests.
Compiling helloworld.d
```
export CC=gcc11 ; ldc2 helloworld.d
```
works fine.

Compiling helloworld.d
```
export CC=clang ; ldc2 helloworld.d
```
returns:
```
d: error: undefined hidden symbol: __start___minfo
>>> referenced by test.d
>>>               test.o:(ldc.register_dso)

ld: error: undefined hidden symbol: __stop___minfo
>>> referenced by test.d
>>>               test.o:(ldc.register_dso)
clang: error: linker command failed with exit code 1 (use -v to 
see invocation)
Error: /usr/bin/clang failed with status: 1
```

So I have a workaround by fixing it to gcc