Update the configuration for Travis CI and AppVeyor CI

Simplify the test matrix on Travis CI to reduce the testing time.

Use CI_CMAKE_TOOLCHAIN_FILE on AppVeyor CI.

.appveyor.yml

@@ -45,8 +45,8 @@ install:
   - 'if "%TOOLCHAIN%"=="vstudio" C:\tools\vcpkg\vcpkg.exe integrate install'
 
 before_build:
-  - 'if "%TOOLCHAIN%"=="vstudio" set CI_CMAKE_VARS=-DCMAKE_TOOLCHAIN_FILE=C:\tools\vcpkg\scripts\buildsystems\vcpkg.cmake'
   - 'if "%TOOLCHAIN%"=="vstudio" set CI_CMAKE_GENERATOR=Visual Studio 17 2022'
+  - 'if "%TOOLCHAIN%"=="vstudio" set CI_CMAKE_TOOLCHAIN_FILE=C:\tools\vcpkg\scripts\buildsystems\vcpkg.cmake'
   - 'if "%TOOLCHAIN%"=="vstudio" if "%ARCH%"=="x86" set CI_CMAKE_GENERATOR_PLATFORM=Win32'
   - 'if "%TOOLCHAIN%"=="vstudio" if "%ARCH%"=="x64" set CI_CMAKE_GENERATOR_PLATFORM=x64'
   - 'if "%TOOLCHAIN%"=="vstudio" if "%ARCH%"=="arm64" set CI_CMAKE_GENERATOR_PLATFORM=ARM64'

.travis.yml

@@ -9,10 +9,6 @@ os:
   - linux
   - osx
 
-compiler:
-  - clang
-  - gcc
-
 env:
   - AUTOMATION=cmake CI_NO_TEST=1
   - AUTOMATION=cmake CI_CMAKE_VARS="-DPNG_HARDWARE_OPTIMIZATIONS=ON" CI_SANITIZERS="address,undefined"
@@ -26,20 +22,14 @@ env:
 matrix:
   include:
     - os: osx
-      compiler: cc
       env: AUTOMATION=cmake CI_CMAKE_GENERATOR=Xcode
-  exclude:
-    - os: freebsd
-      compiler: gcc
-    - os: osx
-      compiler: gcc
 
 before_script:
+  - 'if test "$TRAVIS_OS_NAME" = "linux"; then COMPILER="gcc"; else COMPILER="clang"; fi'
+  - 'export CI_MAKEFILES="scripts/makefile.std scripts/makefile.$COMPILER"'
+  - 'export CI_MAKE_FLAGS="-j2"'
   - 'export CI_CMAKE_BUILD_FLAGS="--parallel 2"'
   - 'export CI_CTEST_FLAGS="--parallel 2"'
-  - 'export CI_MAKE_FLAGS=-j2'
-  - 'export CI_CC=$TRAVIS_COMPILER'
-  - 'export CI_MAKEFILES="scripts/makefile.$TRAVIS_COMPILER scripts/makefile.std"'
 
 script:
   - './ci/ci_verify_$AUTOMATION.sh'