Makefile: use shell for-loop rather than Make's foreach loop during install

Makefile: use shell for-loop rather than Make's foreach loop during install

The install target uses a foreach loop to generate a single long shell
command line to handle installation of the built-in git commands.  The
maximum length of the argument list varies by platform, and this use of
foreach quickly grows the length of the argument list.  Current git can
exceed the default maximum argument list length on IRIX 6.5 of 20480
depending on the installation path.

Rather than using make's foreach loop to pre-generate the shell command
line, use a shell for-loop and allow the shell to iterate through each of
the built-in commands.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>