As discussed in bug 28327, the fromfp functions changed type in C23 (compared to the version in TS 18661-1); they now return the same type as the floating-point argument, instead of intmax_t / uintmax_t. As with other such incompatible changes compared to the initial TS 18661 versions of interfaces (the types of totalorder functions, in particular), it seems appropriate to support only the new version as an API, not the old one (although many programs written for the old API might in fact work wtih the new one as well).
The Linux kernel ABI specifies that the vector registers are not preserved across system calls, but the __SYSCALL_CLOBBERS macro doesn't mention them.
This makes the final file truly hybrid: Externally the file is a regular, non-fragmented file, but internally, the fragmented form also exists un-overwritten. To make any use of that, first, the fragments need to be muxed in a position independent form, i.e.
C23 makes assert into a variadic macro to handle cases of an argument that would be interpreted as a single function argument but more than one macro argument (in particular, compound literals with an unparenthesized comma in an initializer list); this change was made by N2829.
The graph string is either freed or attached to the filtergraph, so it's best to not leave a dangling pointer with the caller.
SSSE3 is already quite old (introduced 2006 for Intel, 2011 for AMD), so that the overwhelming majority of our users (particularly those that actually update their FFmpeg) will be using the SSSE3 versions.