Makefile: Use pkg-config for systems where ncurses is not libcurses.so (fixes #66)

[hartwork]

Fixes #66

I'm happy to adjust and discuss.

[tenox7]

Running make on macOS returns:

/bin/sh: pkg-config: command not found

[hartwork]

@tenox7 two thoughts on that:

• they could install it via homebrew
• we could try something like pkg-config --libs ncurses 2>/dev/null || echo '-lcurses -ltinfo' instead?

[hartwork]

@tenox7 updated now to demo the fallback approach.

[tenox7]

that looks better, let me test it a bit :)

[hartwork]

@tenox7 any news?

[tenox7]

BTW the variable expansion is done when CC command is invoked

$ make
cc -O2 -pipe -Wall -Wextra  ttyplot.c `pkg-config --libs ncurses 2>/dev/null || echo '-lcurses -ltinfo'` -o ttyplot

[hartwork]

@tenox7 yes, is that a problem? I'm not sure about the message here.

[tenox7]

I guess it's not a problem on modern systems.