Random buildbot failures detecting ambiguities in LinearAlgebra

[kmsquire]

Two recent pull requests (#31633 and #31632) have randomly resulted in the same buildbot error, thrown while detecting ambiguities in LinearAlgebra.

The errors occured on different architectures (linux32 and macos64). Other tests in the same PRs (mostly) passed (or if they failed, it was for different reasons).

      From worker 9:	Error During Test at /buildworker/worker/tester_linux32/build/share/julia/stdlib/v1.3/LinearAlgebra/test/ambiguous_exec.jl:4
      From worker 9:	  Test threw exception
      From worker 9:	  Expression: detect_ambiguities(LinearAlgebra; imported=true, recursive=true) == []
      From worker 9:	  TypeError: in TypeVar, in upper bound, expected Type, got Core.Compiler.Iterators.Filter{getfield(Core.Compiler, Symbol("##254#261")){Core.Compiler.IdDict{Int32,Int32}},Array{Int32,1}}
      From worker 9:	  Stacktrace:
      From worker 9:	   [1] typeintersect at ./reflection.jl:560 [inlined]
      From worker 9:	   [2] #isambiguous#23(::Bool, ::typeof(Base.isambiguous), ::Method, ::Method) at ./reflection.jl:1266
      From worker 9:	   [3] #isambiguous at ./none:0 [inlined]
      From worker 9:	   [4] #detect_ambiguities#30(::Bool, ::Bool, ::Bool, ::typeof(detect_ambiguities), ::Module) at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.3/Test/src/Test.jl:1439
      From worker 9:	   [5] (::getfield(Test, Symbol("#kw##detect_ambiguities")))(::NamedTuple{(:imported, :recursive),Tuple{Bool,Bool}}, ::typeof(detect_ambiguities), ::Module) at ./none:0
      From worker 9:	   [6] top-level scope at /buildworker/worker/tester_linux32/build/share/julia/stdlib/v1.3/LinearAlgebra/test/ambiguous_exec.jl:4
      From worker 9:	   [7] include at ./boot.jl:328 [inlined]
      From worker 9:	   [8] include_relative(::Module, ::String) at ./loading.jl:1094
      From worker 9:	   [9] include(::Module, ::String) at ./Base.jl:31
      From worker 9:	   [10] exec_options(::Base.JLOptions) at ./client.jl:295
      From worker 9:	   [11] _start() at ./client.jl:464
      From worker 9:	  
      From worker 9:	ERROR: Error while loading expression starting at /buildworker/worker/tester_linux32/build/share/julia/stdlib/v1.3/LinearAlgebra/test/ambiguous_exec.jl:4
      From worker 9:	caused by [exception 1]
      From worker 9:	There was an error during testing
      From worker 9:	running testset LinearAlgebra/lapack...

Links to logs of failures:
https://build.julialang.org/#/builders/13/builds/1602/steps/2/logs/stdio (line 2776)
https://build.julialang.org/#/builders/69/builds/632/steps/2/logs/stdio (line 330)

[kmsquire]

In the first log above, Worker 2 also failed, with output at lines 253-3361. The start of the failure has

      From worker 2:	running testset LinearAlgebra/dense...
      From worker 2:	Internal error: encountered unexpected error in runtime:
      From worker 2:	TypeError(func=:Union, context="", expected=Type, got=<?#0xdc94bad8::<?#0xdc94bae0::<?#0xdc94bac0::<circular reference @-1>>>>)
      From worker 2:	rec_backtrace at /buildworker/worker/package_linux32/build/src/stackwalk.c:94
      From worker 2:	record_backtrace at /buildworker/worker/package_linux32/build/src/task.c:210 [inlined]
      From worker 2:	jl_throw at /buildworker/worker/package_linux32/build/src/task.c:417
      From worker 2:	jl_type_error_rt at /buildworker/worker/package_linux32/build/src/rtutils.c:118
      From worker 2:	jl_type_error at /buildworker/worker/package_linux32/build/src/rtutils.c:125
      From worker 2:	jl_type_union at /buildworker/worker/package_linux32/build/src/jltypes.c:476
      From worker 2:	intersect_all at /buildworker/worker/package_linux32/build/src/subtype.c:2490
...

[kmsquire]

This second type of error is also cropping up on other buildbot builds, e.g. https://build.julialang.org/#/builders/65/builds/915/steps/2/logs/stdio (#31700)

      From worker 6:	running testset LinearAlgebra/diagonal...
      From worker 6:	record_backtrace at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\task.c:210 [inlined]
      From worker 6:	jl_throw at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\task.c:417
      From worker 6:	jl_type_error_rt at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\rtutils.c:118
      From worker 6:	jl_type_error at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\rtutils.c:125
      From worker 6:	jl_type_union at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\jltypes.c:476
      From worker 6:	intersect_all at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\subtype.c:2490
      From worker 6:	intersect_aside at /home/Administrator/buildbot/worker/package_win32/build/src/home/Administrator/buildbot/worker/package_win32/build/src\subtype.c:1541

[kmsquire]

Possibly related: #31703 (memory corruption during type intersection, which looks quite similar to the second error above.)

[kmsquire]

Probably fixed by #31747