The compiler-specific hardware floating-point support is compiled in, using the plattform "netx90_app_hardfp" in the waf-scripts.
The legacy option to modify compiler flags on your own is to open the file "C:\ProgramData\Hilscher GmbH\netX Studio CDT\BuildTools\waf\waflib\extras\hilscher_toolchains.py" and edit in the function "configure_device_netx90" the relevant flags as needed.