cmake: do find Git for Windows' shell interpreter

By default, Git for Windows does not install its `sh.exe` into the
`PATH`. However, our current `CMakeLists.txt` expects to find a shell
interpreter in the `PATH`.

So let's fall back to looking in the default location where Git for
Windows _does_ install a relatively convenient `sh.exe`:
`C:\Program Files\Git\bin\sh.exe`

Helped-by: Øystein Walle <oystwa@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/buildsystems/CMakeLists.txt

@@ -41,7 +41,7 @@ cmake_minimum_required(VERSION 3.14)
 #set the source directory to root of git
 set(CMAKE_SOURCE_DIR ${CMAKE_CURRENT_LIST_DIR}/../..)
 
-find_program(SH_EXE sh)
+find_program(SH_EXE sh PATHS "C:/Program Files/Git/bin")
 if(NOT SH_EXE)
 	message(FATAL_ERROR "sh: shell interpreter was not found in your path, please install one."
 			"On Windows, you can get it as part of 'Git for Windows' install at https://gitforwindows.org/")