Profile: by default, don't initialize with more than 10M samples (even if there are multiple threads); also, fix the Profile tests when multithreading is enabled

[DilumAluthge]

Fixes #42252

[DilumAluthge]

Okay, so in its current state, this PR fixes the Profile tests on linux64.

However, there are still failures on linux32.

Here are the `linux32` failures (click to expand):

      From worker 5:	┌ Warning: The profile data buffer is full; profiling probably terminated
      From worker 5:	│ before your program finished. To profile for longer runs, call
      From worker 5:	│ `Profile.init()` with a larger buffer and/or larger delay.
      From worker 5:	└ @ Profile /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Profile/src/Profile.jl:510
      From worker 5:	┌ Warning: The profile data buffer is full; profiling probably terminated
      From worker 5:	│ before your program finished. To profile for longer runs, call
      From worker 5:	│ `Profile.init()` with a larger buffer and/or larger delay.
      From worker 5:	└ @ Profile /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Profile/src/Profile.jl:510
Profile                             (5) |         failed at 2021-09-15T09:20:47.555
Test Failed at /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:110
  Expression: n_ == def_n * Threads.nthreads()
   Evaluated: 134217728 == 160000000
Error During Test at /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:120
  Got exception outside of a @test
  InexactError: check_top_bit(UInt32, -2147483648)
  Stacktrace:
    [1] throw_inexacterror(f::Symbol, #unused#::Type{UInt32}, val::Int32)
      @ Core ./boot.jl:607
    [2] check_top_bit
      @ ./boot.jl:621 [inlined]
    [3] toUInt32
      @ ./boot.jl:720 [inlined]
    [4] UInt32
      @ ./boot.jl:761 [inlined]
    [5] convert
      @ ./number.jl:7 [inlined]
    [6] cconvert
      @ ./essentials.jl:417 [inlined]
    [7] init(n::Int32, delay::Float64; limitwarn::Bool)
      @ Profile /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Profile/src/Profile.jl:77
    [8] init(; n::Int32, delay::Float64, limitwarn::Bool)
      @ Profile /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Profile/src/Profile.jl:62
    [9] macro expansion
      @ /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:130 [inlined]
   [10] macro expansion
      @ /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Test/src/Test.jl:1321 [inlined]
   [11] top-level scope
      @ /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:121
   [12] include
      @ ./Base.jl:416 [inlined]
   [13] macro expansion
      @ /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/test/testdefs.jl:24 [inlined]
   [14] macro expansion
      @ /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Test/src/Test.jl:1321 [inlined]
   [15] macro expansion
      @ /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/test/testdefs.jl:23 [inlined]
   [16] macro expansion
      @ ./timing.jl:368 [inlined]
   [17] runtests(name::String, path::String, isolate::Bool; seed::UInt128)
      @ Main /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/test/testdefs.jl:21
   [18] (::Distributed.var"#106#108"{Distributed.CallMsg{:call_fetch}})()
      @ Distributed /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Distributed/src/process_messages.jl:278
   [19] run_work_thunk(thunk::Distributed.var"#106#108"{Distributed.CallMsg{:call_fetch}}, print_error::Bool)
      @ Distributed /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Distributed/src/process_messages.jl:63
   [20] macro expansion
      @ /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Distributed/src/process_messages.jl:278 [inlined]
   [21] (::Distributed.var"#105#107"{Distributed.CallMsg{:call_fetch}, Distributed.MsgHeader, Sockets.TCPSocket})()
      @ Distributed ./task.jl:411
Error During Test at /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:148
  Test threw exception
  Expression: getline(values(fdictc)) == getline(values(fdict0)) + 2
  MethodError: no method matching +(::Nothing, ::Int32)
  Closest candidates are:
    +(::Any, ::Any, !Matched::Any, !Matched::Any...) at operators.jl:655
    +(!Matched::T, ::T) where T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8} at int.jl:87
    +(!Matched::T, ::Integer) where T<:AbstractChar at char.jl:237
    ...
  Stacktrace:
   [1] macro expansion
     @ /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Test/src/Test.jl:460 [inlined]
   [2] macro expansion
     @ /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:148 [inlined]
   [3] macro expansion
     @ /cache/build/amdci7-2/julialang/julia-master/usr/share/julia/stdlib/v1.8/Test/src/Test.jl:1321 [inlined]
   [4] top-level scope
     @ /cache/build/amdci7-0/julialang/julia-master/julia-e9e09c705c/share/julia/stdlib/v1.8/Profile/test/runtests.jl:134

The full log is here: https://buildkite.com/julialang/julia-master/builds/3683#00e8a61a-add7-484e-8803-64c8a1b77d76