Thank you, it is now working.
I did as suggested and
- removed the current C:\sysgcc\raspberry directory
- downloaded the latest full SD card and toolchain from your website
- flashed the SD card
- installed the toolchain
- synchronised sysroot (from SD card without doing any updates or upgrades)
- created a new project
- compiled and it worked!
I think I had updated from GCC 6.3.0 to GCC 8.3.0. Whether this caused the problem I don’t know. I had synchronised sysroot with the “Re-download all files” option but this didn’t work.
Thanks again for your guidance.