This article is from the Amiga FAQ, by Ignaz Kellerer with numerous contributions by others.
The inline headers for gcc can be created from the original CBM fd files. See Includes. See Pragmas. They can be created as follows:
CLI> Assign INCLUDE: GCC:os-include CLI> Assign FD: INCLUDE:fd CLI> Makedir INCLUDE:inline CLI> cd USR:bin/geninline CLI> gen31
This will create all inline-headers in `GCC:os-include/inline'. If you have 2.0 headers, use gen20 instead, if you have 3.0, use gen30. OS3.1 (rev 40.13) inline headers are included with the current version of gcc. See Current Version.
NOTE: perl scripts do not handle correctly AmigaDOS include files, which seems to mean they are somewhat broken. This needs some voluntary work ...
There is also another way of generating inline headers, using fd2inline program:
CLI> fd2inline <fd_file> <proto_file>