ROMAN_HUNDREDS, ROMAN_TENS and ROMAN_ONES seem to use syntax, that is not
recognized (any longer?) by flex, so let's expand their definitions.

Index: spl-1.2.1/include/roman_numbers.metaflex
===================================================================
--- spl-1.2.1.orig/include/roman_numbers.metaflex
+++ spl-1.2.1/include/roman_numbers.metaflex
@@ -1,5 +1,5 @@
 ROMAN_THOUSANDS m+
-ROMAN_HUNDREDS  (c(d|m)|dc{0,3}|c{1,3})
-ROMAN_TENS      (x(l|c)|lx{0,3}|x{1,3})
-ROMAN_ONES      (i(v|x)|vi{0,3}|i{1,3})
+ROMAN_HUNDREDS  (c(d|m|c?c?)|dc?c?c?)
+ROMAN_TENS      (x(l|c|x?x?)|lx?x?x?)
+ROMAN_ONES      (i(v|x|i?i?)|vi?i?i?)
 ROMAN_NUMBER    {ROMAN_ONES}|{ROMAN_TENS}{ROMAN_ONES}?|{ROMAN_HUNDREDS}{ROMAN_TENS}?{ROMAN_ONES}?|{ROMAN_THOUSANDS}{ROMAN_HUNDREDS}?{ROMAN_TENS}?{ROMAN_ONES}?
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<tr><td><span title='2018-03-01 22:21:00 +0100'>2018-03-01</span></td><td><a href='/guix/commit/gnu/packages/libftdi.scm?id=4f5452ab3aaccb17a6e4e3c9b3029cd1ed408102'>gnu: libftdi: Use HTTPS home page.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/libftdi.scm (libftdi)[home-page]: Use HTTPS.
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<tr><td><span title='2018-02-28 22:58:23 +0100'>2018-02-28</span></td><td><a href='/guix/commit/gnu/packages/libftdi.scm?id=0828bd82bd72bf198ee8374f45aca2e3db96daf9'>gnu: libftdi: Update to 1.4.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/libftdi.scm (libftdi): Update to 1.4.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>