Can't build current HEAD with --enable-perl-xs on macOS

[Dario Gjorgjevski]

Building on macOS with --enable-perl-xs fails with:

    $ TEXINFO_DEV_SOURCE=1 top_srcdir="$(top_srcdir)"
top_builddir="$(top_builddir)" $(PERL) ../../tp/texi2any.pl -o
texi2any_internals.info texi2any_internals.texi
    dyld[99271]: dyld_image_path_containing_address(0x10d5c7000) =>
'$(top_builddir)/tp/Texinfo/XS/.libs/XSParagraph.so'
    dyld[99271]: _dyld_is_memory_immutable(0x10d5c7000, 28) => 0
    dyld[99271]:       dlopen(XSParagraph.so) => 0x7ff918400670
    dyld[99271]: dlsym(0x7ff918400670, "boot_Texinfo__Convert__Paragraph")
    dyld[99271]:      dlsym("boot_Texinfo__Convert__Paragraph") => 0x10d5c9e50
    dyld[99271]: missing symbol called

Bisecting, I see that the last commit I am able to build successfully
is e665d4eaba.  I am doing an in-source build, if that changes
anything.  (I see that there have been some changes to accommodate for
out-of-source builds.)

Running the offending command with TEXINFO_XS=omit seems to work.
TEXINFO_XS=debug does not show anything interesting, only successes
followed by the "missing symbol called" failure.

Best regards,
Dario