The Full Debug Symbol (FDS) work established the use of objcopy/gobjcopy to produce symbols files as part of the build process. That work did not cover any of the requirements for cross-compilation and so when cross-compiling FDS generation is simply disabled.
Cross-compilation environments should define ALT_OBJCOPY to point to the correct tool for generating symbols and so the explicit disabling of FDS should be removed.
The default objcopy is now assumed to be on the ALT_COMPILER_PATH when cross-compiling. That can still be overridden by setting ALT_OBJCOPY.
There was also some cleanup to reduce the number of time the FDS logic gets executed.