configure & compiler warning cleanup

• configure: Use LT_INIT from libtool 2 instead of deprecated AC_PROG_LIBTOOL
• Add X.Org's standard C warning flags to AM_CFLAGS
• Fix 4 -Wdiscarded-qualifiers warnings
• Fix warning: ‘NVDMAKickoffCallback’ defined but not used [-Wunused-function]
• Fix warning: ‘NVPatternROP’ defined but not used [-Wunused-const-variable=]
• Fix -Wdiscarded-qualifiers warning in G80PreInit
• Fix warning: no previous prototype for ‘G80ExaInit’ [-Wmissing-prototypes]