git: Fix bug building git for Linuxbrew
git: Fix bug building git for Linuxbrew

Fix bug building git without Homebrewed perl for Linuxbrew

Closes Homebrew/linuxbrew#392

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