[roll] Roll fuchsia [bootsvc] Define a userspace clock fixed at zero.

UTC reads currently use a userspace clock if one is available and
fallback to the kernel if not. This fallback and the kernel clock are
being removed via RFC-0008.

Bootsvc starts before component manager and so does not have access to
the userspace clock component manager creates. Bootfs reads UTC to
set file times and these reads will begin to fail when the fallback is
removed (note that the time they return today is incorrect, being near
zero in very early boot, near backstop a few seconds later, and only
actually reaching true UTC tens of seconds later if a network is
available).

This CL defines a new userspace clock for bootsvc fixed at zero, meaning
bootfs UTC reads will not fail and file times will always be reported
as zero.

Further information is available at go/fxb-60095-discussion.

Original-Bug: 90095
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/484555
Original-Revision: b754090a3a2b8b89a9bfca70222462a724a52463
GitOrigin-RevId: 98a5efbaef03cbae684b8fafc58835f2339fee0c
Change-Id: I5e6a029f4f2c5c6cf63d8039b45ebeef63c2486c
diff --git a/stem b/stem
index e036130..fc70d8d 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
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