Generated (precompiled) function names changing

[Magnus Holmgren, Millnet/Lysator/Debian/Mensa @ Pike developers forum]

When building both the current stable 8.0 and 9.0.11, *sometimes* the
C code gets regenerated from .cmod (by precompile.pike, I guess) and
then the macros in src/modules/Gmp/mpq.c change names from f_mpq_* to
f_Gmp_mpq_* (and similarly in other modules), which in that case
causes compilation to fail because mpq.cmod contains references to
some of the generated function names, e.g. f_mpq_get_int(0) in
cast(string). Any idea how this is happening and if it's supposed to
happen and the function calls should be changed to match?