gflags.exe is copied to \reactos\bin, conflicts with regression tests

When building an ISO with rosapps and rostests enabled, gflags.exe is copied to \reactos\bin.
This directory is de-facto reserved for regression tests, and rosautotest.exe tries to run all executables in there as tests. It currently errors out immediately due to gflags.exe.

Please move it to system32 or wherever Windows puts it.
If we instead need a different directory for regression tests, please let me know.