atkmm: Fix test for Linuxbrew
atkmm: Fix test for Linuxbrew

Only add -lintl on macOS.

Signed-off-by: Bob W. Hogg <rwhogg@linux.com>

Closes Linuxbrew/homebrew-core#3390.

Signed-off-by: Shaun Jackman <b580dab3251a9622aba3803114310c23fdb42900@gmail.com>

rwhogg/homebrew-core,LinuxbrewTestBot/homebrew-core,Linuxbrew/homebrew-core,maxim-belkin/homebrew-core,maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core