core: main: remove all the spam about including make files

Change-Id: Ifd2ef0e239d16b169c572472416c2c31df62a367
(cherry picked from commit a53bf194bba486ce2a188e4f7a1bbaaab0539113)
envsetup: do not print an error if complete fails

complete is a bashism; so it will fail on other shells. Avoid printing
an error if that is the case.

Change-Id: Id6d6311792f409cc3a697c7a2bb003863f1afe60
(cherry picked from commit 99a16eefb11e2e0a2ac4a523b8d6f1132d967765)
envsetup: drop unnecesary exports

export -f is a bashism and we don't actually need it, so lets remove it.

Change-Id: I9228cef0c4a9543b3d34fdc39a368ad0238431e2
(cherry picked from commit e8790829ffacdb473ee4284b98cc979ac9dd191f)
envsetup: Mark zsh as compatible

Basic functionality has been tested on zsh 5.0.2 and has been found to
work correctly.

Change-Id: I02e5e3bedf56b43104c280d9737ae7b334357643
(cherry picked from commit 1b6880fab69a6560fab3e417659e563d60a08426)
Support building with GNU make 4.0

* It works just fine, no need for the warning.

Change-Id: Ifa2ab17454edfcd8b7840a7534f70576286f2864
(cherry picked from commit e7f104271eb3a4dff8dd49a452e979b358fa3c92)