[swiftpm] Add preset for SwiftPM Linux build

[benlangmuir]

Intended for the Linux smoke test job that currently does not use a
preset.

[benlangmuir]

preset=buildbot_swiftpm_linux_platform,tools=RA,stdlib=RA
@swift-ci Please test with preset Linux

[benlangmuir]

@swift-ci please smoke test

[benlangmuir]

13:48:03 /home/buildnode/jenkins/workspace/swift-PR-Linux-preset/branch-master/swift/utils/build-script: note: using preset "buildbot_swiftpm_linux_platform,tools=RA,stdlib=RA", which expands to
13:48:03
13:48:03 /home/buildnode/jenkins/workspace/swift-PR-Linux-preset/branch-master/swift/utils/build-script --test --validation-test '--lit-args=-v --time-tests' --compiler-vendor=apple --reconfigure --verbose-build --build-ninja --build-swift-stdlib-unittest-extra --build-subdir=buildbot_incremental --release --assertions --swiftpm --xctest --foundation --libdispatch --llbuild --skip-test-swift --skip-test-cmark --skip-test-llbuild --skip-test-libdispatch --skip-test-foundation --skip-test-xctest

[aciidgh]

Are there other tests we should be skipping?

[benlangmuir]

Not that I know of. The job currently passes:

--skip-test-swift --skip-test-llbuild --skip-test-libdispatch --skip-test-cmark --skip-test-foundation --skip-test-xctest

which is the same, but reordered.

[gottesmm]

NOTE: Eventually this will need to be changed so we run the integration tests. This is a good first step though!