Update Exercises/4.2 - Exec and system/solutions/Ex06-Execve.c, Exercises/4.2 - Exec and system/solutions/Ex07-System.c

Update Exercises/4.2 - Exec and system/solutions/Ex07-System.c, Exercises/4.2 - Exec and system/solutions/Ex04-Execvp.c

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	new file:   4 - Inter Process Communication.pdf
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	renamed:    Slides/2 - OS History.pdf -> Slides/1-OS History.pdf
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	new file:   Slides/3a-Cross-Compiling.pdf
	new file:   Slides/3b-ELF.pdf
	new file:   Slides/3c-Makefiles.pdf