sim_main: Print clear error in case CreateProcessA fails #353

Job	Run time
test / matrix-prep-bazelversion	6s
test / matrix-prep-os	2s
test / test (ubuntu-latest, 8.0.0, ., true)	4m 36s
test / test (ubuntu-latest, 7.3.1, ., true)	4m 36s
	9m 20s

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