Link with -ldl on GNU Hurd

Debian GNU/Hurd uses the GNU C library.

Signed-off-by: Peter Colberg <peter@colberg.org>

cgit.mk

@@ -54,7 +54,7 @@ endif
 endif
 
 # Add -ldl to linker flags on systems that commonly use GNU libc.
-ifneq (,$(filter $(uname_S),Linux GNU/kFreeBSD))
+ifneq (,$(filter $(uname_S),Linux GNU GNU/kFreeBSD))
 	CGIT_LIBS += -ldl
 endif