Ruby extconf.rb is creating a wrong make file

I have been trying to build ibm_db driver on my own with ruby 2.6.5 + devkit

When I run ruby extconf.rb it creates make file but make file contains path related to unix but I am running it on windows.

ERROR:-

$ mingw32-make
mingw32-make: *** No rule to make target '/C/Ruby26/include/ruby-2.6.0/ruby.h', needed by 'ibm_db.o'.  Stop.

how to solve this issue?

Thanks in advance,
Akhil