Makefile: add YOSYS_VER and friends to CXXFLAGS for plugin compat che…

[widlarizer]

As Yosys interfaces change, plugin developers may decide to stay compatible with a broad spectrum of versions. We will provide per-interface feature defines of some sort, but as a fallback in case we don't, I'm adding Makefile variable YOSYS_VER to CXXFLAGS so that yosys-config reports reports it to the plugin sources when building them. It also splits YOSYS_VER to YOSYS_MAJOR, YOSYS_MINOR, YOSYS_COMMIT which don't need quoting and can be used as integers. For example:

$ cat a.cpp
#include <stdio.h>
#include <string.h>

int main() {
	if (!strcmp(YOSYS_VER, "0.47+86"))
		printf("Yay %d\n", YOSYS_MINOR);
	else
		printf("Nay\n");

	printf(YOSYS_VER "\n");
	return 0;
}
$ yosys-config --exec --cxx --cxxflags --ldflags a.cpp
$ ./a.out
Yay 47
0.47+86

This could also be the base for requiring plugins to report the version they were built against.