libswift: on macOS, make the default build mode bootstrapping-with-hostlibs

This is much faster than the full "bootstrapping" mode.
On linux, the default stays "bootstrapping", because "bootstrapping-with-hostlibs" is not supported.

In CI:
* Build two presets with "bootstrapping", so that this mode is tested on macOS at least on some bots.
* Do the macOS smoke test also with "bootstrapping-with-hostlibs". It only adds ~30 sec compared to "hosttools" which was used previously.

Author: eeckstein

utils/build-presets.ini

@@ -192,7 +192,9 @@ skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
 
-libswift=bootstrapping-with-hostlibs
+# Test the full bootstrapping on at least some jobs
+# (the default is bootstrapping-with-hostlibs)
+libswift=bootstrapping
 
 [preset: buildbot,tools=RA,stdlib=RD,test=non_executable]
 mixin-preset=
@@ -216,7 +218,9 @@ skip-test-tvos-host
 skip-test-watchos-host
 check-incremental-compilation
 
-libswift=bootstrapping-with-hostlibs
+# Test the full bootstrapping on at least some jobs
+# (the default is bootstrapping-with-hostlibs)
+libswift=bootstrapping
 
 [preset: buildbot,tools=R,stdlib=RD,test=non_executable]
 mixin-preset=
@@ -653,9 +657,6 @@ skip-build-benchmarks
 # Skip playground tests
 skip-test-playgroundsupport
 
-# Don't do bootstrapping to speed up the build
-libswift=hosttools
-
 [preset: buildbot_incremental,tools=RA,stdlib=RD,smoketest=macosx,flto]
 mixin-preset=buildbot_incremental,tools=RA,stdlib=RD,smoketest=macosx
 build-subdir=buildbot_incremental
@@ -1563,9 +1564,6 @@ build-swift-stdlib-unittest-extra
 
 libcxx
 
-# Don't do bootstrapping to speed up the build
-libswift=hosttools
-
 # Build llbuild & swiftpm here
 llbuild
 swiftpm

utils/build-script-impl

@@ -362,7 +362,11 @@ function to_libswift_buildmode() {
             echo "OFF"
             ;;
         true | TRUE | 1 | "")
-            echo "BOOTSTRAPPING"
+            if [[ "$(uname -s)" == "Darwin" ]] ; then
+              echo "BOOTSTRAPPING-WITH-HOSTLIBS"
+            else
+              echo "BOOTSTRAPPING"
+            fi
             ;;
         *)
             echo `toupper $1`

utils/build_swift/build_swift/driver_arguments.py

@@ -546,8 +546,6 @@ def create_argument_parser():
 
     option('--libswift', store('libswift_mode'),
            choices=['off', 'hosttools', 'bootstrapping', 'bootstrapping-with-hostlibs'],
-           const='hosttools',
-           default=None,
            help='The libswift build mode. For details see libswift/README.md')
 
     # -------------------------------------------------------------------------