Make file changes requeired to compile on windows

I kept hitting shader compile problems on Windows.
I ended up having to alter the Makefile at /renderer/src/shaders/Makefile to fix some file path problems on Windows.

Here's the section I changed:

$(OUT)/d3d/%.vert.h:` d3d/%.hlsl $(MINIFY_STAMP)
	@mkdir -p "$(OUT)/d3d"
	fxc -nologo -D VERTEX   -I "$(OUT)" $(FXC_DEBUG_FLAG) -T vs_5_0 -Fh "$@" "$<"

$(OUT)/d3d/%.frag.h: d3d/%.hlsl $(MINIFY_STAMP)
	@mkdir -p "$(OUT)/d3d"
	fxc -nologo -D FRAGMENT -I "$(OUT)" $(FXC_DEBUG_FLAG) -T ps_5_0 -Fh "$@" "$<"

$(OUT)/d3d/render_atlas_stroke.frag.h: d3d/render_atlas.hlsl $(MINIFY_STAMP)
	@mkdir -p "$(OUT)/d3d"
	fxc -nologo -D FRAGMENT -D ATLAS_FEATHERED_STROKE $(FXC_DEBUG_FLAG) -I "$(OUT)" -T ps_5_0 -Fh "$@" "$<"

$(OUT)/d3d/render_atlas_fill.frag.h: d3d/render_atlas.hlsl $(MINIFY_STAMP)
	@mkdir -p "$(OUT)/d3d"
	fxc -nologo -D FRAGMENT -D ATLAS_FEATHERED_FILL  $(FXC_DEBUG_FLAG) -I "$(OUT)" -T ps_5_0 -Fh "$@" "$<"

$(OUT)/d3d/root.sig.h: d3d/root.sig
	@mkdir -p "$(OUT)/d3d"
	fxc -nologo -I "$(OUT)" -T rootsig_1_1 -E ROOT_SIG -Fh "$@" "$<"

The setup_windows_dev.bat also points to the wrong make path, so after running the bat script, I then changed the path to the correct one using: set PATH=C:\msys64\usr\bin;%PATH%

Otherwise, I generally followed the instructions in #68

Start with setup_windows_dev.bat and renderer/src/shaders/Makefile, then reproduce the shader compilation problems on Windows using the setup instructions from issue #68. Done means the Windows setup script finds the intended make path and the shader Makefile compiles the listed Direct3D shaders without manual edits.