git-gui: silence install recipes under "make -s"

git-gui: silence install recipes under "make -s"

Several install and uninstall recipes embed "echo" calls that fire as
part of the recipe itself, so the install banners (DEST, INSTALL,
LINK, REMOVE) were visible whenever the variables expand non-empty.

Guard the whole "ifndef V" block on "-s" so the loud variants are
selected only when "-s" is absent and V=1 is unset. The existing
"-s" check also had its findstring arguments in the wrong order
(needle "-s" never fit in haystack "s"), so swap them while moving
the check to wrap the block.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>