test-codegen: make jl_dump_compiles test more reliable (#23486)

This was a flaky test, and it's not entirely clear what it was testing.

Common failure was:
        FAILURE
    Error in testset codegen:
    Test Failed
      Expression: tempty == true
       Evaluated: false == true
    ERROR: LoadError: Test run finished with errors
    while loading C:\projects\julia\julia-a661736be5\share\julia\test\runtests.jl, in expression starting on line 29
    Command exited with code 1

test/codegen.jl

@@ -51,13 +51,9 @@ end
 function test_jl_dump_compiles()
     tfile = tempname()
     io = open(tfile, "w")
+    @eval(test_jl_dump_compiles_internal(x) = x)
     ccall(:jl_dump_compiles, Void, (Ptr{Void},), io.handle)
-    eval(@noinline function test_jl_dump_compiles_internal(x)
-        if x > 0
-            test_jl_dump_compiles_internal(x-1)
-        end
-        end)
-    test_jl_dump_compiles_internal(1)
+    @eval test_jl_dump_compiles_internal(1)
     ccall(:jl_dump_compiles, Void, (Ptr{Void},), C_NULL)
     close(io)
     tstats = stat(tfile)
@@ -71,8 +67,9 @@ end
 function test_jl_dump_compiles_toplevel_thunks()
     tfile = tempname()
     io = open(tfile, "w")
+    topthunk = expand(Main, :(for i in 1:10; end))
     ccall(:jl_dump_compiles, Void, (Ptr{Void},), io.handle)
-    eval(expand(Main, :(for i in 1:10 end)))
+    Core.eval(Main, topthunk)
     ccall(:jl_dump_compiles, Void, (Ptr{Void},), C_NULL)
     close(io)
     tstats = stat(tfile)