Migrate from Travis CI to GitHub Actions

The old Travis CI .org service has been throttled for a while now and is
said to be shutting down completely next week.

This migrates the Travis CI build jobs to GitHub Actions, with minor
changes.

- The trailing whitespace detection has been removed for now.
- The libegl1-mesa-dev dependency for Wayland has been removed as it
  appears to no longer be necessary for building.

.github/workflows/build.yml

@@ -2,18 +2,18 @@ name: Build
 on:
     pull_request:
     push:
-        branches: [ ci, master, latest, 3.3-stable ]
+        branches: [ ci, master, 3.3-stable ]
 permissions:
     statuses: write
     contents: read
+env:
+    CC: clang
+    CFLAGS: -Werror
 
 jobs:
     build-linux-x11-clang:
         name: X11 (Linux, Clang)
         runs-on: ubuntu-latest
-        env:
-            CC: clang
-            CFLAGS: -Werror
         steps:
             - uses: actions/checkout@v2
             - name: Install dependencies
@@ -34,9 +34,6 @@ jobs:
     build-linux-wayland-clang:
         name: Wayland (Linux, Clang)
         runs-on: ubuntu-latest
-        env:
-            CC: clang
-            CFLAGS: -Werror
         steps:
             - uses: actions/checkout@v2
             - name: Install dependencies
@@ -57,9 +54,6 @@ jobs:
     build-linux-null-clang:
         name: Null (Linux, Clang)
         runs-on: ubuntu-latest
-        env:
-            CC: clang
-            CFLAGS: -Werror
         steps:
             - uses: actions/checkout@v2
             - name: Install dependencies
@@ -81,7 +75,6 @@ jobs:
         name: Cocoa (macOS, Clang)
         runs-on: macos-latest
         env:
-            CFLAGS: -Werror
             MACOSX_DEPLOYMENT_TARGET: 10.8
         steps:
             - uses: actions/checkout@v2
@@ -96,21 +89,3 @@ jobs:
             - name: Build shared library
               run: cmake --build build-shared --parallel
 
-    build-windows-win32-vs2019:
-        name: Win32 (Windows, VS2019)
-        runs-on: windows-latest
-        env:
-            CFLAGS: /WX
-        steps:
-            - uses: actions/checkout@v2
-
-            - name: Configure static library
-              run: cmake -S . -B build-static -G "Visual Studio 16 2019"
-            - name: Build static library
-              run: cmake --build build-static --parallel
-
-            - name: Configure shared library
-              run: cmake -S . -B build-shared -G "Visual Studio 16 2019" -D BUILD_SHARED_LIBS=ON
-            - name: Build shared library
-              run: cmake --build build-shared --parallel
-