Clean up wrapper script/CFLAGS and friends mix on Windows

Our mix of wrapper scripts and usage of CFLAGS/LDFLAGS when compiling on Windows has grown over the years to a point where it gets confusing. We should get back to sanity here.

We needed the wrapper scripts to pass down all required flags to the depths of the Firefox build system, but meanwhile those scripts are used almost everywhere and CFLAGS/LDFLAGS additionally sometimes.

One option boklm brought up would be to use the CFLAGS/LDFLAGS defined in rbm.conf and enable those scripts only during Firefox's build.

Another just get rid of those wrapper scripts and fix the missing pieces in Firefox if those are still there.

At any rate, we should document where we need them in the first place to avoid lengthy digging in case someone is wondering in the future or now, while looking at our build scripts.