Your branch is not against Mir trunk so it can't be merged into lp:mir. Also, you've put Requires instead of Requires.private in the .pc file. This would causes something using mir-client-platform-mesa to link against libmirclient which is not required as the platform headers just contain structs and defines.
I've sponsored your mesa change to wily, thanks!
Your branch is not against Mir trunk so it can't be merged into lp:mir. Also, you've put Requires instead of Requires.private in the .pc file. This would causes something using mir-client- platform- mesa to link against libmirclient which is not required as the platform headers just contain structs and defines.
I've made an alternate branch lp:~robert-ancell/mir/mir-client-platform-mesa-dev-depends with these fixes and an additional missing package dependency but feel free to update your branch if you would prefer to merge that.