[preset] Add toolchain-benchmarks to swiftpm presets

Author: benlangmuir

utils/build-presets.ini

@@ -1509,6 +1509,9 @@ assertions
 # Downstream projects that import llbuild+SwiftPM.
 sourcekit-lsp
 
+toolchain-benchmarks
+skip-test-toolchain-benchmarks
+
 skip-test-llbuild
 
 #===------------------------------------------------------------------------===#
@@ -1525,6 +1528,9 @@ assertions
 # Downstream projects that import llbuild+SwiftPM.
 sourcekit-lsp
 
+toolchain-benchmarks
+skip-test-toolchain-benchmarks
+
 skip-test-llbuild
 
 #===------------------------------------------------------------------------===#