Avoid any linker specific compiler command line options for syntaxOnly builds.
Avoid any linker specific compiler command line options for syntaxOnly builds.

This fixes an apparent regression, where the documentation build fails with "Unrecognized extension", because a "." file name is specified on the compiler command line. The "." is supposed to be the path to the target binary of a dependency, but in syntaxOnly mode, there are no binaries at all.

grogancolin/dub,rjframe/dub,Geod24/dub,D-Programming-Language/dub,gedaiu/dub,Flamaros/dub