Use standard autotools means to detect X11

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.

configure.ac

@@ -199,16 +199,26 @@ else
 fi
 fi
 
-# checking for Xlib, Xfixes
-AC_CHECK_HEADER([X11/Xlib.h], [],
-  [AC_MSG_ERROR([please install libx11-dev or libX11-devel])])
+AC_PATH_XTRA
+if test "x$no_x" == "xyes"; then
+  AC_MSG_ERROR([please install libx11-dev or libX11-devel])
+fi
+
+save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS $X_CFLAGS"
+
+# checking for Xfixes
 AC_CHECK_HEADER([X11/extensions/Xfixes.h], [],
   [AC_MSG_ERROR([please install libx11-dev and libxfixes-dev or libXfixes-devel])],
   [#include <X11/Xlib.h>])
+
+# checking for Xrandr
 AC_CHECK_HEADER([X11/extensions/Xrandr.h], [],
   [AC_MSG_ERROR([please install libxrandr-dev or libXrandr-devel])],
   [#include <X11/Xlib.h>])
 
+CFLAGS="$save_CFLAGS"
+
 libdir="${libdir}/xrdp";
 if test "x${prefix}" = "xNONE" ; then
 sysconfdir="/etc";

genkeymap/Makefile.am

@@ -1,9 +1,12 @@
+AM_CFLAGS = $(X_CFLAGS)
 
 bin_PROGRAMS = \
   xrdp-genkeymap
 
 xrdp_genkeymap_SOURCES = genkeymap.c evdev-map.c
 
+xrdp_genkeymap_LDFLAGS = \
+  $(X_LIBS)
+
 xrdp_genkeymap_LDADD = \
-  -L/usr/X11R6/lib \
-  -lX11
+  $(X_PRE_LIBS) -lX11 $(X_EXTRA_LIBS)

sesman/chansrv/Makefile.am

@@ -40,6 +40,8 @@ AM_CPPFLAGS = \
   -I$(top_srcdir)/common \
   $(EXTRA_INCLUDES)
 
+AM_CFLAGS = $(X_CFLAGS)
+
 sbin_PROGRAMS = \
   xrdp-chansrv
 
@@ -60,10 +62,10 @@ xrdp_chansrv_SOURCES = \
   chansrv_common.c
 
 xrdp_chansrv_LDFLAGS = \
+  $(X_LIBS) \
   $(EXTRA_FLAGS)
 
 xrdp_chansrv_LDADD = \
-  -L/usr/X11R6/lib \
   $(top_builddir)/common/libcommon.la \
-  -lX11 -lXfixes -lXrandr \
+  $(X_PRE_LIBS) -lXfixes -lXrandr -lX11 $(X_EXTRA_LIBS) \
   $(EXTRA_LIBS)

sesman/tools/Makefile.am

@@ -9,6 +9,8 @@ AM_CPPFLAGS = \
   -I$(top_srcdir)/sesman/libscp \
   -I$(top_srcdir)/sesman
 
+AM_CFLAGS = $(X_CFLAGS)
+
 bin_PROGRAMS = \
   xrdp-sesrun \
   xrdp-sesadmin \
@@ -46,6 +48,8 @@ xrdp_sesadmin_LDADD = \
   $(top_builddir)/common/libcommon.la \
   $(top_builddir)/sesman/libscp/libscp.la
 
+xrdp_xcon_LDFLAGS = \
+  $(X_LIBS)
+
 xrdp_xcon_LDADD = \
-  -L/usr/X11R6/lib \
-  -lX11
+  $(X_PRE_LIBS) -lX11 $(X_EXTRA_LIBS)