git-sh-setup: define workaround wrappers before they are used

git-sh-setup: define workaround wrappers before they are used

Recently we tweaked this scriptlet to let mingw port redefine "pwd" to
always return Windows-style path, but the code to do so came after the
first use of "pwd" to set up $GIT_DIR shell variable.

Move the block to define these workaround wrappers, so that everything
everything that executes when the scriptlet is dot-sourced uses the
replacements.

Noticed-by: Ramsay Jones
Signed-off-by: Junio C Hamano <gitster@pobox.com>