Running leanpkg build lib breaks on Windows with MSYS2

[tydeu]

Prerequisites

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Description

Trying to build a Lean 4 package as a library with leanpkg build lib results in a missing leanc.exe error on Windows with MSYS2. This likely is due to the fact that it is expecting it to be named leanc.exe instead of its actual name leanc (i.e. with no extension).

Steps to Reproduce

On Windows with MSYS2:

1. Create a new directory (ex. mkdir hello)
2. Initialize a Lean 4 package in the directory (ex. cd hello; leanpkg init Hello)
3. Run leanpkg build lib on the package
4. Observe the error

An error like the following should occur:

configuring Hello 0.1
> sh -c "<home>\.elan\toolchains\leanprover--lean4---nightly-2021-05-23\bin/leanmake" LEAN_OPTS="" LEAN_PATH="././build" lib >&2    # in directory .
lean  -o "build/Hello.olean" --c="build/temp/Hello.c.tmp" Hello.lean
mv "build/temp/Hello.c.tmp" "build/temp/Hello.c"
leanc -c -o build/temp/Hello.o build/temp/Hello.c -O3 -DNDEBUG
←[31m←[1merror: ←[0mtoolchain 'leanprover/lean4:nightly-2021-05-23' does not have the binary `<home>\.elan\toolchains\leanprover--lean4---nightly-2021-05-23\bin\leanc.exe`
make: *** [<home>\.elan\toolchains\leanprover--lean4---nightly-2021-05-23\bin/../share/lean/lean.mk:73: build/temp/Hello.o] Error 1
uncaught exception: external command exited with status 2

Expected behavior:

I would expect leanpkg build lib to work on Windows with MSYS2

Actual behavior:

It fails to run leanc due to expecting it to be named leanc.exe instead of leanc.

Reproduces how often:

Always.

Versions

Windows 20H2
Lean (version 4.0.0-nightly-2021-05-23, commit 28b055463fbc, Release)

I am using MSYS2 bash (MinGW 64-bit) as my terminal:

GNU bash, version 5.1.4(1)-release (x86_64-pc-msys)
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

Additional Information

None.