F37 Change: MinGW UCRT target (Self-Contained Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/F37MingwUCRT

== Summary ==

This proposal is to add the UCRT target & support from Fedora to the
MinGW cross-toolchains.

== Owner ==
* Name: [[User:elmarco| Marc-André Lureau]]
* Email: [e-mail]

== Detailed Description ==

The current mingw32 and mingw64 cross-toolchains provided by Fedora
target the MSVCRT (Microsoft Visual C++ Runtime). Since Visual Studio
15 & Windows 10, the default and recommended runtime is UCRT. See also
[https://www.msys2.org/docs/environments/#msvcrt-vs-ucrt MSVCRT vs
UCRT].

A new toolchain target triple `x86_64-w64-mingw32ucrt` and associated
binaries will be added.

Fedora MinGW macros will be provided to target UCRT, with ucrt64-*
prefix (ex: `ucrt64-meson`)

mingw-* libraries will be progressively adjusted to add the produced
ucrt64-* binaries.

Since mingw-*.spec are very repetitive and cumbersome to modify (each
mingw32, mingw64, ucrt package has to be defined manually, and this is
tedious and error-prone), a custom MinGW/Fedora tool or solution will
be proposed. In the meantime, packages can be modified to add manually
the new target.

[https://lists.fedoraproject.org/archives/list/[e-mail]/...
UCRT plans on  [e-mail] ]

== Benefit to Fedora ==

This change will allow to cross-compile projects to Windows with the
up to date C runtime & headers, and better c99 support. This should
allow to more easily mix binaries produced from different versions or
compilers as well.

== Scope ==

* Proposal owners:
** update the mingw filesystem, binutils, headers, gcc & winpthreads packages
** bootstrap the new toolchain
** propose a solution to simplify library packaging with the different targets
** update some common library packages, such as mingw-zlib
* Other developers:
** Progressively adjust the mingw-* packages to produce ucrt64-
packages, following the updated guidelines.
* Release engineering:
* Policies and guidelines:
https://fedoraproject.org/wiki/Packaging:MinGW packaging guideline
will be adjusted.
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives:

== Upgrade/compatibility impact ==

None

== How To Test ==

<pre>
$ x86_64-w64-mingw32ucrt-gcc test.c

$ /usr/bin/mingw-objdump -p a.exe | grep DLL
 vma:            Hint    Time      Forward  DLL       First
    DLL Name: KERNEL32.dll
    DLL Name: api-ms-win-crt-time-l1-1-0.dll
    DLL Name: api-ms-win-crt-math-l1-1-0.dll
    DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
    DLL Name: api-ms-win-crt-environment-l1-1-0.dll
    DLL Name: api-ms-win-crt-private-l1-1-0.dll
    DLL Name: api-ms-win-crt-heap-l1-1-0.dll
    DLL Name: api-ms-win-crt-locale-l1-1-0.dll
    DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
    DLL Name: api-ms-win-crt-string-l1-1-0.dll
</pre>

== User Experience ==

Windows binaries produced by Fedora cross-toolchain will target a more
modern and compatible C runtime, bringing hopefully better
compatibility & safety.

== Dependencies ==

None

== Contingency Plan ==

* Contingency mechanism:  N/A (not a System Wide Change)
* Contingency deadline: N/A (not a System Wide Change)
* Blocks release? No (not a System Wide Change)

== Documentation ==

N/A (not a System Wide Change)

== Release Notes ==

The new MinGW toolchain and tools are available to compile binaries
targeting the Windows UCRT.