[preset] Add presets for llbuild smoke test jobs

On macOS, this is functionally equivalent to the existing CI job
configurtion. On Linux, it adds a few options inherited from
buildbot_incremental_base that weren't already there, and enables
assertions.

rdar://55195297

Author: benlangmuir

utils/build-presets.ini

@@ -1498,10 +1498,35 @@ assertions
 llbuild
 swiftpm
 
-dash-dash
+skip-test-swift
+skip-test-cmark
+
+#===------------------------------------------------------------------------===#
+# Test llbuild on Linux builder
+#===------------------------------------------------------------------------===#
+
+[preset: buildbot_llbuild_linux_platform,tools=RA,stdlib=RA]
+mixin-preset=buildbot_incremental_base
+
+build-subdir=buildbot_incremental
+
+# Build Release without debug info, because it is faster to build.
+release
+assertions
+
+# Build llbuild & swiftpm here
+llbuild
+swiftpm
+
+xctest
+foundation
+llbuild
 
 skip-test-swift
 skip-test-cmark
+skip-test-foundation
+skip-test-libdispatch
+skip-test-xctest
 
 #===------------------------------------------------------------------------===#
 # Test Swift Packages