Currently we see errors like

[   48s] In file included from <command-line>:
[   48s] ../sysdeps/ieee754/ldbl-96/s_modfl.c:72:29: error: conflicting types
for built-in function 'modff64x'; expected '_Float64x(_Float64x,  _Float64x *)'
[-Werror=builtin-declaration-mismatch]
[   48s]    72 | libm_alias_ldouble (__modf, modf)
[   48s]       |                             ^~~~

which seems to be fixed in master with f66780ba46805760a328f01967836416b06c93ca
by passing the appropriate -fno-builtin-XXX flags for the build of those
files.

That change needs to be picked to our glibc package.