gcc@4.9: Add postinstall for Linuxbrew
gcc@4.9: Add postinstall for Linuxbrew

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