Optimize Makefile for pvsneslib

[kobenairb]

Hi all,

In the same way, a small optimization for the Makefile used by pvsneslib/.

The changes are:

The export statements can be moved inside the variable definition, and we don't need to export TOPDIR since it's not used outside this Makefile.

The @echo command in the docs target can be made into a single line to avoid unnecessary output.

The if statement in the docs target can be simplified by using @[ -f warn.log ] && cat warn.log to output the warn.log file.

This version uses "$(MAKE)" instead of "make" to ensure that the make command is correctly overridden if the user specifies a different make command.

It also uses "@rm" instead of "rm" and "@mkdir" instead of "mkdir" to suppress command echoing, and removes unnecessary semicolons at the end of some commands.

The mkdir command will fail if the lib directory already exists, which can be the case if the Makefile is run multiple times. To avoid this issue, the -p option is used with the mkdir command to create the directory only if it does not exist.

[RetroAntho]

Thanks !