Alas, it looked promising: ran for an hour or two, generating almost 7000 lines of console output, then said this
==> Finished making: mingw-w64-kicad-git r9689.5bbb4489b-1 (Mon, Mar 5, 2018 1:09:33 PM)
==> Installing package mingw-w64-x86_64-kicad-git with pacman -U...
looking for conflicting packages...
Packages (1) mingw-w64-x86_64-kicad-git-r9689.5bbb4489b-1
Total Installed Size: 3316.33 MiB
Thereafter it worked for a few minutes longer and said this
-- Looking for C:/MinGW/home/BrianP/src/MINGW-packages/mingw-w64-kicad-git/src/build-i686-w64-mingw32/CMakeFiles/CMakeTmp/CheckSymbolExists.cxx
-- Looking for C:/MinGW/home/BrianP/src/MINGW-packages/mingw-w64-kicad-git/src/build-i686-w64-mingw32/CMakeFiles/CMakeTmp/CheckSymbolExists.cxx - not found
which I find odd: why is it trying to make i686 instead of 64 bit?
Anyhow a bit later it threw out
CMake Error at CMakeLists.txt:583 (find_package):
By not providing "FindOCE.cmake" in CMAKE_MODULE_PATH this project has
asked CMake to find a package configuration file provided by "OCE", but
CMake did not find one.
Could not find a package configuration file provided by "OCE" (requested
version 0.16) with any of the following names:
Add the installation prefix of "OCE" to CMAKE_PREFIX_PATH or set "OCE_DIR"
to a directory containing one of the above files. If "OCE" provides a
separate development package or SDK, be sure it has been installed.
When I look for these files they are not found
$ find /home -name "o*.cmake"
I figured I'd try make OCE (why not) so I typed
==> ERROR: pkgname is not allowed to start with a hyphen.
==> ERROR: An unknown error has occurred. Exiting...
I am going to completely reinstall Msys2 and try again ...