[LLVM] Update MC maintainer (#119571)

We currently list Jim Grosbach as the maintainer for the MC layer --
however, he hasn't been involved in LLVM for about ten years.

I'd like to propose MaskRay as the replacement. I think he has done
most of the substantial MC work in recent times.

Author: nikic

llvm/Maintainers.md

@@ -143,8 +143,8 @@ [email protected] (email), [qcolombet](https://github.com/qcolombet) (G
 
 #### MC layer
 
-James Grosbach \
-[email protected] (email)
+Fangrui Song \
+[email protected] (email), [MaskRay](https://github.com/MaskRay) (GitHub)
 
 #### Windows codegen
 
@@ -456,6 +456,7 @@ Paul C. Anagnostopoulos ([email protected], [Paul-C-Anagnostopoulos](https://git
 Justin Bogner ([email protected], [bogner](https://github.com/bogner)) -- SelectionDAG \
 Evan Cheng ([email protected]) -- Parts of code generator not covered by someone else \
 Renato Golin ([email protected], [rengolin](https://github.com/rengolin)) -- ARM backend \
+James Grosbach ([email protected]) -- MC layer \
 Anton Korobeynikov ([email protected], [asl](https://github.com/asl)) -- ARM EABI \
 Chad Rosier ([email protected]) -- FastISel \
 Hans Wennborg ([email protected], [zmodem](https://github.com/zmodem)) -- Release management \