Bug 1723956 - Make --without-sysroot work again. r=firefox-build-system-reviewers,mhentges

Also make it not bootstrap a host sysroot.

Differential Revision: https://phabricator.services.mozilla.com/D121815

build/moz.configure/toolchain.configure

@@ -918,20 +918,27 @@ def provided_program(env_var, when=None):
 
 
 @template
-def sysroot_path(host_or_target):
+def sysroot_path(host_or_target, target_sysroot=None):
+    assert target_sysroot or host_or_target is target
+    bootstrap_target_when = target_is_linux
     if host_or_target is host:
         host_or_target_str = "host"
         opt = "--with-host-sysroot"
         env = "HOST_SYSROOT"
         when = depends(host)(lambda h: h.kernel == "Linux")
-        bootstrap_when = when
+        # Only bootstrap a host sysroot when using a bootstrapped target sysroot
+        # or when the target doesn't use a bootstrapped sysroot in the first place.
+        @depends(when, bootstrap_target_when, target_sysroot.bootstrapped)
+        def bootstrap_when(when, bootstrap_target_when, bootstrapped):
+            return when and (bootstrapped or not bootstrap_target_when)
+
     else:
         assert host_or_target is target
         host_or_target_str = "target"
         opt = "--with-sysroot"
         env = "SYSROOT"
         when = target_is_linux_or_wasi
-        bootstrap_when = target_is_linux
+        bootstrap_when = bootstrap_target_when
 
     option(
         opt,
@@ -943,7 +950,10 @@ def sysroot_path(host_or_target):
 
     sysroot_input = depends(opt, when=when)(lambda x: x)
     bootstrap_sysroot = depends(bootstrap_when, sysroot_input)(
-        lambda bootstrap, input: bootstrap and not input
+        # Only bootstrap when no flag was explicitly given (either --with or --without)
+        lambda bootstrap, input: bootstrap
+        and not input
+        and input.origin == "default"
     )
 
     @depends(
@@ -983,7 +993,7 @@ def system_lib_option(name, *args, **kwargs):
             )
 
 
-host_sysroot_path = sysroot_path(host).path
+host_sysroot_path = sysroot_path(host, target_sysroot_path).path
 target_sysroot_path = target_sysroot_path.path