A C-based alternative for compiling ZIL? I don't believe there's one that works. The two options for compiling ZIL code are to run ZILF on a modern system or to run ZILCH on a PDP-10 emulator.
The good news is you don't need to install any C# development tools if you use the prepackaged binaries, since they're standalone executables.
Right - that's because ZIL was more or less a _superset_ of MDL.
ZILCH (Infocom's compiler) provided all the functions of MDL, _plus_ a bunch of new ones that manipulated data structures which were then used to generate assembly code for the Z-machine.
One of those new functions, ROUTINE, accepted code written in a domain-specific language resembling a stripped-down MDL, which was then translated into Z-machine instructions. But that domain-specific language isn't synonymous with ZIL: other functions that were inarguably part of ZIL, like OBJECT and SYNTAX, are not part of that domain-specific language.
IMO, the only reasonable definition of ZIL is "the language accepted by a ZIL compiler", which (depending on whether you look at ZILCH or ZILF) is either a superset of MDL or an overlapping set.
Author of ZILF here. I wouldn't say that ZIL "does not have support for custom macros", because ZIL never existed in a form independent of MDL. There's no such thing as "MDL macros that were not available in ZIL", because there was never a version of ZIL that didn't have macros.