* m4/manywarnings.m4m, m4/warnings.m4: Import GNULIB warnings
modules
* m4/spice-compile-warnings.m4: Define SPICE_COMPILE_WARNINGS
* configure.ac: Replace compile warning check with a call to
SPICE_COMPILE_WARNINGS
* client/Makefile.am: Use WARN_CXXFLAGS instead of WARN_CFLAGS
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>