Makefile enhancements#25

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adriweb wants to merge 3 commits intonumworks:masterfrom

Commits on Jul 14, 2022

makefile: support C files, and fix C++ flags variable name.
adriweb
committed
makefile: -lm needs to be added at the end of the link flags.
adriweb
committed
makefile: minor cleanup and add an "all" target for IDE compatibility
adriweb
committed