message: Clear up build matrix and add GCC 8
diff: // Our build matrix. The keys are the operating system labels and the values
  // are lists of tool labels.
  buildMatrix = [
  - // Release and debug builds for various OS/Compiler combinations.
  - ['Linux', [
  + // Debug builds with ASAN + logging for various OS/compiler combinations.
  + ['unix', [
  + cmakeArgs: '-D CAF_LOG_LEVEL=4 '
  + + '-D CAF_ENABLE_ADDRESS_SANITIZER:BOOL=yes',
  builds: ['debug'],
  - tools: ['gcc4.8', 'gcc4.9', 'gcc5.1', 'gcc6.3', 'gcc7.2', 'clang'],
  + tools: ['gcc4.8', 'gcc4.9', 'gcc5', 'gcc6', 'gcc7', 'gcc8', 'clang'],
  ]],
  + // One release build per supported OS. FreeBSD and Windows have the least
  + // testing outside Jenkins, so we also explicitly schedule debug builds.
  ['Linux', [
  builds: ['release'],
  tools: ['gcc', 'clang'],
  ]],
  ['macOS', [
  - builds: ['debug', 'release'],
  - tools: ['gcc', 'clang'],
  + builds: ['release'],
  + tools: ['clang'],
  ]],
  ['FreeBSD', [
  builds: ['debug', 'release'],
  @@ -24,30 +28,8 @@ buildMatrix = [
  builds: ['debug', 'release'],
  tools: ['msvc'],
  ]],
  - // Additional builds with logging enabled.
  - ['Linux', [
  - cmakeArgs: '-D CAF_LOG_LEVEL=4',
  - builds: ['debug', 'release'],
  - tools: ['gcc'],
  - ]],
  - ['macOS', [
  - cmakeArgs: '-D CAF_LOG_LEVEL=4',
  - builds: ['debug', 'release'],
  - tools: ['clang'],
  - ]],
  - // Additional debug builds with ASAN enabled.
  - ['Linux', [
  - cmakeArgs: '-D CAF_ENABLE_ADDRESS_SANITIZER:BOOL=yes',
  - builds: ['debug'],
  - tools: ['gcc'],
  - ]],
  - ['macOS', [
  - cmakeArgs: '-D CAF_ENABLE_ADDRESS_SANITIZER:BOOL=yes',
  - builds: ['debug'],
  - tools: ['clang'],
  - ]],
  - // Additional debug build with coverage.
  - ['Linux', [
  + // One Additional build for coverage reports.
  + ['unix', [
  cmakeArgs: '-D CAF_ENABLE_GCOV:BOOL=yes '
  + '-D CAF_NO_EXCEPTIONS:BOOL=yes '
  + '-D CAF_FORCE_NO_EXCEPTIONS:BOOL=yes',
  