Eigen Compiler Suite

With the following addition to the Makefile:

   else ifdef MSYSTEM
    CP := cp -f
    RM := rm -f
    TC := touch

    PRG :=
    DIR = $1
    DIRP = $1
    ESC = \$(strip $1)
    NUL := /dev/null

    ENVIRONMENT := windows.cpp

    ifdef CommonProgramFiles(x86)
        HOSTENVIRONMENTS := win32 win64
    else
        HOSTENVIRONMENTS := dos win32
    endif

    ifeq "$(MSYSTEM)" "CLANG64" 
        toolchain := clang
    else
        toolchain := gcc
    endif

I was able to build the code with the CLANG compiler.
GCC ended with a error:

In file included from mapsearch.cpp:21:
utilities.hpp:407:29: error: template-id not allowed for destructor in C++20 [-Werror=template-id-cd
tor]
  407 | inline ECS::Restore<Value>::~Restore<Value> ()
      |                             ^
compilation terminated due to -Wfatal-errors.
cc1plus.exe: all warnings being treated as errors
make: *** [makefile:722: tools/mapsearch.o] Error 1

GCC version is 14.1.0
I did not investigate this any further.

CLANG completes the build without any problems.

Running the tests run mostly clean except for:

Results of test suite 'doccheck.tst':
number of tests: 38
succeeded tests: 19
failed tests:    19

Usually getting software to work on MSYS2 platforms involves some
grinding, but here it works directly from a Makefile. Quite impressive.