build-presets: enable testing of libswift bootstrapping on two CI bots

Enable the "bootstrapping" build mode on buildbot_incremental,tools=RA,stdlib=RA
and the "bootstrapping-with-hostlibs" mode on buildbot,tools=RA,stdlib=RD

Author: eeckstein

utils/build-presets.ini

@@ -192,6 +192,7 @@ skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
 
+libswift=bootstrapping-with-hostlibs
 
 [preset: buildbot,tools=RA,stdlib=RD,test=non_executable]
 mixin-preset=
@@ -371,6 +372,8 @@ install-swiftpm
 install-swift-driver
 install-libcxx
 
+libswift=bootstrapping
+
 [preset: buildbot_incremental,tools=RA,stdlib=RA,apple_silicon]
 mixin-preset=buildbot_incremental,tools=RA,stdlib=RA