lnav: add re2c as head build dependency.
lnav: add re2c as head build dependency.

Recent changes in lnav have added re2c as a build time dependency.
Fix the homebrew formula to reflect the same.

Closes #43918.

Signed-off-by: Dominyk Tiller <53e438f55903875d07efdd98a8aaf887e7208dd3@gmail.com>

kwilczynski/homebrew,kwilczynski/homebrew,kwilczynski/homebrew,kwilczynski/homebrew