Another nice solution, Pablo, thank you.

The macron is shifted a little too far to the left and needs a raisebox to
align the top of the C with the M.

https://tex.stackexchange.com/a/364027/2148

Hans' solution is pretty close. Here's what the LaTeX folks made:

https://i.stack.imgur.com/CRaam.png

I've tweaked some numbers to get a pretty decent result for this particular
font:

\starttext
M{\dontleavehmode{\raisebox{.45ex}\hbox{\scale[sx=1.1,sy=1.1]{c}}}}\hskip-1ex
{\dontleavehmode{\raisebox{0ex}\hbox{\hl[.4]}}Anulty

Mc̲Anulty
\stoptext