May I suggest the following trivial patch?
diff -r ff9e591a2aa5 src/lib/Makefile.am
--- a/src/lib/Makefile.am Sun Nov 18 21:44:22 2007 +0200
+++ b/src/lib/Makefile.am Tue Nov 20 00:29:04 2007 +0600
@@ -4,9 +4,9 @@ BUILT_SOURCES = unicodemap.c
EXTRA_DIST = unicodemap.c unicodemap.pl
-unicodemap.c:
+$(srcdir)/unicodemap.c:
test -f UnicodeData.txt || wget
http://www.unicode.org/Public/UNIDATA/UnicodeData.txt
- perl unicodemap.pl < UnicodeData.txt > $@
+ perl $(srcdir)/unicodemap.pl < UnicodeData.txt > $@
liblib_a_SOURCES = \
backtrace-string.c \
