[PATCH] Deprecate TileGX port

[Peter Maydell]

Deprecate our TileGX target support:
 * we have no active maintainer for it
 * it has had essentially no contributions (other than tree-wide cleanups
   and similar) since it was first added
 * the Linux kernel dropped support in 2018, as has glibc

Note the deprecation in the manual, but don't try to print a warning
when QEMU runs -- printing unsuppressable messages is more obtrusive
for linux-user mode than it would be for system-emulation mode, and
it doesn't seem worth trying to invent a new suppressible-error
system for linux-user just for this.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
We discussed dropping this target last year:
 https://patchew.org/QEMU/20191012071210.13632-1-philmd@redhat.com/
and before that in 2018, when Chen told us he didn't have time
to work on tilegx any more:
https://lists.gnu.org/archive/html/qemu-devel/2018-03/msg03955.html
Given that tilegx is no longer in upstream Linux I think it makes sense
to finally deprecate-and-drop our linux-user support for it.

 docs/system/deprecated.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 3a255591c34..e9097e089bb 100644
--- a/docs/system/deprecated.rst
+++ b/docs/system/deprecated.rst
@@ -387,6 +387,17 @@ The above, converted to the current supported format::
 
   json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
 
+linux-user mode CPUs
+--------------------
+
+``tilegx`` CPUs (since 5.1.0)
+'''''''''''''''''''''''''''''
+
+The ``tilegx`` guest CPU support (which was only implemented in
+linux-user mode) is deprecated and will be removed in a future version
+of QEMU. Support for this CPU was removed from the upstream Linux
+kernel in 2018, and has also been dropped from glibc.
+
 Related binaries
 ----------------
 
-- 
2.20.1