Enable lightweight assertions in Linux packages

utils/build-presets.ini

@@ -455,10 +455,31 @@ build-subdir=buildbot_incremental_special_leaks
 dash-dash
 swift-runtime-enable-leak-checker=1
 
+#===------------------------------------------------------------------------===#
+# Package Builders
+#===------------------------------------------------------------------------===#
+
+# A mixin that enables 'lightweight' assertions that don't slow down the
+# compiler significantly.
+[preset: mixin_lightweight_assertions]
+assertions
+
+# FIXME: This should be:
+# no-assertions
+# swift-assertions
+# ... but our tests are expecting assertions to be either on or off everywhere.
+
+dash-dash
+
+# AST verifier slows down the compiler significantly.
+swift-enable-ast-verifier=0
+
 #===------------------------------------------------------------------------===#
 # Linux Builders
 #===------------------------------------------------------------------------===#
 [preset: mixin_linux_installation]
+mixin-preset=mixin_lightweight_assertions
+
 llbuild
 swiftpm
 xctest