Add support for MSYS2

[Eon Jeong (eonj)]

With this patch, Z3 is compiled via MSYS shell and toolchain of MSYS2. (MINGW32 shell and MINGW64 shell is not yet cared.)

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[Christoph M. Wintersteiger (wintersteiger)]

Our scripts already supported mingw, see is_cygwin_mingw() and IS_CYGWIN_MINGW. Do we really want -D_CYGWIN when compiling via mingw?

[Eon Jeong (eonj)]

It's MSYS2, MinTTY subsystem running MinGW-w64 toolchain, based on recent Cygwin fork. It's different from traditional cmd.exe running MinGW toolchain.

When I run ./configure in the MSYS shell, I got this error:

Traceback (most recent call last):
  File "scripts/mk_make.py", line 21, in <module>
    mk_makefile()
  File "/home/Eon/Development/z3/scripts/mk_util.py", line 2575, in mk_makefile
    mk_config()
  File "/home/Eon/Development/z3/scripts/mk_util.py", line 2474, in mk_config
    raise MKException('Unsupported platform: %s' % sysname)
mk_exception.MKException: 'Unsupported platform: MSYS_NT-10.0'

What I got with ./configure in MINGW64 shell is:

Writing build/Makefile
Copied Z3Py example 'all_interval_series.py' to 'build/python'
Copied Z3Py example 'example.py' to 'build/python'
Copied Z3Py example 'socrates.py' to 'build/python'
Copied Z3Py example 'visitor.py' to 'build/python'
Makefile was successfully generated.
  compilation mode: Release
  platform: x86
To build Z3, open a [Visual Studio Command Prompt], then
type 'cd C:/Users/Eon/Development/z3/build && nmake'

Remark: to open a Visual Studio Command Prompt, go to: "Start > All Programs > Visual Studio > Visual Studio Tool

You're right, we may not want -D_CYGWIN in MSYS shell really, but this is what worked and I made a PR. I wish I can make a better patch later on.

[Eon Jeong (eonj)]

Christoph M. Wintersteiger (@wintersteiger) My conclusion is, in short, it's good to set -D_CYGWIN in build script for current source code when compiling in MSYS2. If you think the macro name is inappropriate for MSYS2, every appearance of the name _CYGWIN should be modified in source code.

[Christoph M. Wintersteiger (wintersteiger)]

This is not about the appropriateness of the macro name. On the MSYS2 platform we are not supposed to behave like we do on the Cygwin platform (adding -D_CYGWIN changes the behavior of Z3). Also, we already had support for mingw/msys, we just didn't recognize that particular version string yet.

I'm trying to add another commit to this PR/branch, but GitHub is acting up.