With GCC 7.3 same issue
$ make install
make: Entering directory '/usr/local/contrib/gcc-7.3.0'
/bin/sh ./mkinstalldirs /usr/local /usr/local
make: Entering directory '/usr/local/contrib/gcc-7.3.0/host-x86_64-unknown-cygwin/fixincludes'
make: *** No rule to make target 'install'. Stop.
make: Leaving directory '/usr/local/contrib/gcc-7.3.0/host-x86_64-unknown-cygwin/fixincludes'
make: *** [Makefile:3725: install-fixincludes] Error 2
make: Leaving directory '/usr/local/contrib/gcc-7.3.0'
make: *** [Makefile:2326: install] Error 2
This is odd as earlier I was able to configure/make/make install GCC 6.3, So what am I missing? A configure option?