GitLab

This commit squashes several commits that remove:

 unnecessary uname calls
 `sh -c'
 BUILT_INS and QUIET_BUILT_IN

    They have no effect, and the `fixup-builtins' and `check-builtins.sh'
    scripts don't even exist.

 RUNTIME_PREFIX

    It's currently never anything but unset, and it's apparently
    only meaningful when Microsoft Windows is the operating system
    (according to the source for git).

 TEST_PROGRAMS
 EXTRA_PROGRAMS
 unused SHELL_PATH_SQ portions
 unused test for V=2
 useless exports

    Only when `V' is undefined (that is, only when the value of `V'
    is empty) is `export V' performed, which just has the effect of
    placing the empty-valued variable `V' in the environment.

    The only other script to make use of `V' is `Documentation/Makefile',
    which only checks whether `V' is undefined (that is, whether the value
    of `V' is empty); hence, the `export V' has no effect whatsoever.

    Similarly, `export QUIET_GEN' is...