Allow redefining pkg-config Makefile command.
Allow redefining pkg-config Makefile command.

Example usage:

$ make CXX=i686-w64-mingw32-g++ PKG_CONFIG=i686-w64-mingw32-pkg-config

antmicro/yosys,SymbiFlow/yosys,SymbiFlow/yosys,cliffordwolf/yosys,swallat/yosys,swallat/yosys,swallat/yosys,SymbiFlow/yosys,cliffordwolf/yosys,antmicro/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,swallat/yosys,swallat/yosys,YosysHQ/yosys,YosysHQ/yosys,swallat/yosys,azonenberg/yosys,YosysHQ/yosys,antmicro/yosys,SymbiFlow/yosys,azonenberg/yosys,azonenberg/yosys,swallat/yosys,YosysHQ/yosys,SymbiFlow/yosys,SymbiFlow/yosys,azonenberg/yosys,antmicro/yosys,antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,azonenberg/yosys,azonenberg/yosys,YosysHQ/yosys,cliffordwolf/yosys,antmicro/yosys,azonenberg/yosys,cliffordwolf/yosys,antmicro/yosys,azonenberg/yosys,cliffordwolf/yosys,SymbiFlow/yosys,cliffordwolf/yosys,azonenberg/yosys,SymbiFlow/yosys,swallat/yosys,swallat/yosys,cliffordwolf/yosys