appveyor.yml: add linux/amd64 build job (#23548)

.golangci.yml

 # This file configures github.com/golangci/golangci-lint.
 
 run:
-  timeout: 3m
+  timeout: 5m
   tests: true
   # default is true. Enables skipping of directories:
   #   vendor$, third_party$, testdata$, examples$, Godeps$, builtin$

appveyor.yml

-os: Visual Studio 2019
 clone_depth: 5
 version: "{branch}.{build}"
+
+image:
+  - Ubuntu
+  - Visual Studio 2019
+
 environment:
   matrix:
-    # We use gcc from MSYS2 because it is the most recent compiler version available on
-    # AppVeyor. Note: gcc.exe only works properly if the corresponding bin/ directory is
-    # contained in PATH.
     - GETH_ARCH: amd64
-      GETH_CC: C:\msys64\mingw64\bin\gcc.exe
-      PATH: C:\msys64\mingw64\bin;C:\Program Files (x86)\NSIS\;%PATH%
+      GETH_MINGW: 'C:\msys64\mingw64'
     - GETH_ARCH: 386
-      GETH_CC: C:\msys64\mingw32\bin\gcc.exe
-      PATH: C:\msys64\mingw32\bin;C:\Program Files (x86)\NSIS\;%PATH%
+      GETH_MINGW: 'C:\msys64\mingw32'
 
 install:
   - git submodule update --init --depth 1
   - go version
-  - "%GETH_CC% --version"
 
-build_script:
-  - go run build\ci.go install -dlgo -arch %GETH_ARCH% -cc %GETH_CC%
+for:
+  # Linux has its own script without -arch and -cc.
+  # The linux builder also runs lint.
+  - matrix:
+      only:
+        - image: Ubuntu
+    build_script:
+      - go run build/ci.go lint
+      - go run build/ci.go install -dlgo
+    test_script:
+      - go run build/ci.go test -dlgo -coverage
 
-after_build:
-  - go run build\ci.go archive -arch %GETH_ARCH% -type zip -signer WINDOWS_SIGNING_KEY -upload gethstore/builds
-  - go run build\ci.go nsis -arch %GETH_ARCH% -signer WINDOWS_SIGNING_KEY -upload gethstore/builds
+  # linux/386 is disabled.
+  - matrix:
+      exclude:
+        - image: Ubuntu
+          GETH_ARCH: 386
 
-test_script:
-  - go run build\ci.go test -dlgo -arch %GETH_ARCH% -cc %GETH_CC% -coverage
+  # Windows builds for amd64 + 386.
+  - matrix:
+      only:
+        - image: Visual Studio 2019
+    environment:
+      # We use gcc from MSYS2 because it is the most recent compiler version available on
+      # AppVeyor. Note: gcc.exe only works properly if the corresponding bin/ directory is
+      # contained in PATH.
+      GETH_CC: '%GETH_MINGW%\bin\gcc.exe'
+      PATH: '%GETH_MINGW%\bin;C:\Program Files (x86)\NSIS\;%PATH%'
+    build_script:
+      - 'echo %GETH_ARCH%'
+      - 'echo %GETH_CC%'
+      - '%GETH_CC% --version'
+      - go run build/ci.go install -dlgo -arch %GETH_ARCH% -cc %GETH_CC%
+    after_build:
+      # Upload builds. Note that ci.go makes this a no-op PR builds.
+      - go run build/ci.go archive -arch %GETH_ARCH% -type zip -signer WINDOWS_SIGNING_KEY -upload gethstore/builds
+      - go run build/ci.go nsis -arch %GETH_ARCH% -signer WINDOWS_SIGNING_KEY -upload gethstore/builds
+    test_script:
+      - go run build/ci.go test -dlgo -arch %GETH_ARCH% -cc %GETH_CC% -coverage