Due to commit 083daa73 ("Import GNULIB framework for checking code style / rules"), gtk-vnc fails when building out-of-source from a release tarball:

$ tar -xJf gtk-vnc-0.5.0.tar.xz
$ cd gtk-vnc-0.5.0
$ mkdir _build
$ cd _build
$ ../configure
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
[...]
configure: creating ./config.status
config.status: creating Makefile
config.status: creating src/Makefile
config.status: creating tools/Makefile
config.status: creating examples/Makefile
config.status: creating plugin/Makefile
config.status: creating po/Makefile.in
config.status: creating vapi/Makefile
config.status: creating gvnc-1.0.pc
config.status: creating gvncpulse-1.0.pc
config.status: creating gtk-vnc-1.0.pc
config.status: creating gtk-vnc-2.0.pc
config.status: creating gtk-vnc.spec
config.status: creating mingw32-gtk-vnc.spec
config.status: creating config.h
config.status: linking ../GNUmakefile to GNUmakefile
config.status: error: ../GNUmakefile: file not found

Note that for in-source builds, configure works as expected.