gcc: Fix style for Linuxbrew
gcc: Fix style for Linuxbrew

C:259: 65: Use $?.exitstatus.nonzero? instead of $?.exitstatus != 0.
C:265: 52: Use $?.exitstatus.nonzero? instead of $?.exitstatus != 0.

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