Use MSYS2 to build GNU libiconv on Windows CI

Author: HertzDevil

.github/workflows/win.yml

@@ -23,12 +23,14 @@ jobs:
       - name: Enable Developer Command Prompt
         uses: ilammy/msvc-dev-cmd@0b201ec74fa43914dc39ae48a89fd1d8cb592756 # v1.13.0
 
-      - name: Set up Cygwin
-        uses: cygwin/cygwin-install-action@f61179d72284ceddc397ed07ddb444d82bf9e559 # v5
+      - name: Set up MSYS2
+        id: msys2
+        uses: msys2/setup-msys2@61f9e5e925871ba6c9e3e8da24ede83ea27fa91f # v2.27.0
         with:
-          packages: make
-          install-dir: C:\cygwin64
-          add-to-path: false
+          msystem: UCRT64
+          update: true
+          install: >-
+            make
 
       - name: Download Crystal source
         uses: actions/checkout@v4
@@ -102,12 +104,14 @@ jobs:
       - name: Enable Developer Command Prompt
         uses: ilammy/msvc-dev-cmd@0b201ec74fa43914dc39ae48a89fd1d8cb592756 # v1.13.0
 
-      - name: Set up Cygwin
-        uses: cygwin/cygwin-install-action@f61179d72284ceddc397ed07ddb444d82bf9e559 # v5
+      - name: Set up MSYS2
+        id: msys2
+        uses: msys2/setup-msys2@61f9e5e925871ba6c9e3e8da24ede83ea27fa91f # v2.27.0
         with:
-          packages: make
-          install-dir: C:\cygwin64
-          add-to-path: false
+          msystem: UCRT64
+          update: true
+          install: >-
+            make
 
       - name: Download Crystal source
         uses: actions/checkout@v4

etc/win-ci/build-iconv.ps1

@@ -14,7 +14,7 @@ rm libiconv.tar.gz
 
 Run-InDirectory $BuildTree {
     $env:CHERE_INVOKING = 1
-    & 'C:\cygwin64\bin\bash.exe' --login "$PSScriptRoot\cygwin-build-iconv.sh" "$Version" "$(if ($Dynamic) { 1 })"
+    & 'C:\msys64\usr\bin\bash.exe' --login "$PSScriptRoot\cygwin-build-iconv.sh" "$Version" "$(if ($Dynamic) { 1 })"
     if (-not $?) {
         Write-Host "Error: Failed to build libiconv" -ForegroundColor Red
         Exit 1