Honor common make variables from the environment
Honor common make variables from the environment

Instead of overriding CFLAGS etc., append required flags.

android-ia/vendor_intel_external_efivar,CyanogenMod/android_vendor_intel_external_efivar,rhboot/efivar,vathpela/efivar-devel,rhboot/efivar,rhinstaller/efivar,rhinstaller/efivar