byteswap-16.h contains a macro used in many programmes. On Ubuntu 18.04 this file was part of the libc6-dev package and installed to /usr/include/x86_64-linux-gnu/bits. With 20.04 this file is no longer included with this package:
$ sudo apt install libc6-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
libc6-dev is already the newest version (2.31-0ubuntu9).
0 upgraded, 0 newly installed, 0 to remove and 51 not upgraded.
$ ls /usr/include/x86_64-linux-gnu/bits/byteswap-16.h
ls: cannot access '/usr/include/x86_64-linux-gnu/bits/byteswap-16.h': No such file or directory
Thus it is no longer possible to compile various programmes:
$ make
make --directory=lib/dglib/lib
make[1]: Entering directory '/home/duque004/git/DGGRID/src/lib/dglib/lib'
make[1]: *** No rule to make target '/usr/include/x86_64-linux-gnu/bits/byteswap-16.h', needed by 'DgTriGrid2DS.o'. Stop.
make[1]: Leaving directory '/home/duque004/git/DGGRID/src/lib/dglib/lib'
make: *** [Makefile:14: lib/dglib/lib] Error 2
I would rather not intervene manually in system folders to get this header file in. Can it be obtained somehow from the repositories?
Update: This seems more a more general problem. I identified two other header files missing from this package (vis-à-vis 18.04): libio.h and _G_config.h.