Use AC_PATH_XTRA to search for X11 in configure.ac. In Makefiles, add
X_CFLAGS to AM_CFLAGS for the source compilation. Add X_LIBS to LDFLAGS.
Add X_PRE_LIBS and X_EXTRA_LIBS to LDADD.
With this patch, X Windows system is correctly detected on Mac OS X.
AM_CPPFLAGS is for flags passed to the preprocessor, such as defines and
includes. AM_CFLAGS is for flags affecting the compiler, such as debug
and optimization settings.
INCLUDES is an obsolete name. Users can pass INCLUDES and break
compilation. AM_CPPFLAGS is more explicit that the flags come from
Automake and should not be overridden.
Pavel Roskin
Philipp Hahn
Jay Sorg
Itamar Reis Peixoto
jsorg71
ilsimo