azure: replace mingw setup with bash

We're about to phase out our Powershell scripts as Azure
Pipelines does in fact support Bash scripts on all platforms. As
a preparatory step, let's replace our MinGW setup script with a
Bash script.

Author: pks-t

azure-pipelines.yml

@@ -91,7 +91,7 @@ jobs:
   displayName: 'Windows (amd64; MinGW)'
   pool: Hosted
   steps:
-  - powershell: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.ps1'
+  - bash: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.sh'
     displayName: Setup
     env:
       TEMP: $(Agent.TempDirectory)
@@ -106,7 +106,7 @@ jobs:
   displayName: 'Windows (x86; MinGW)'
   pool: Hosted
   steps:
-  - powershell: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.ps1'
+  - bash: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.sh'
     displayName: Setup
     workingDirectory: '$(Build.BinariesDirectory)'
     env:

azure-pipelines/nightly.yml

@@ -94,7 +94,7 @@ jobs:
   displayName: 'Windows (amd64; MinGW)'
   pool: Hosted
   steps:
-  - powershell: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.ps1'
+  - bash: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.sh'
     displayName: Setup
     env:
       TEMP: $(Agent.TempDirectory)
@@ -110,7 +110,7 @@ jobs:
   displayName: 'Windows (x86; MinGW)'
   pool: Hosted
   steps:
-  - powershell: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.ps1'
+  - bash: . '$(Build.SourcesDirectory)\azure-pipelines\setup-mingw.sh'
     displayName: Setup
     workingDirectory: '$(Build.BinariesDirectory)'
     env:

azure-pipelines/setup-mingw.ps1

@@ -0,0 +1,15 @@
+#!/bin/sh -e
+
+echo "##############################################################################"
+echo "## Downloading mingw"
+echo "##############################################################################"
+
+case "$ARCH" in
+	amd64)
+		MINGW_URI="https://bintray.com/libgit2/build-dependencies/download_file?file_path=mingw-w64-x86_64-8.1.0-release-win32-seh-rt_v6-rev0.zip";;
+	x86)
+		MINGW_URI="https://bintray.com/libgit2/build-dependencies/download_file?file_path=mingw-w64-i686-8.1.0-release-win32-sjlj-rt_v6-rev0.zip";;
+esac
+
+curl -s -L "$MINGW_URI" -o "$TEMP"/mingw-"$ARCH".zip
+unzip -q "$TEMP"/mingw-"$ARCH".zip -d "$TEMP"