Merge AM_CFLAGS and INCLUDES info AM_CPPFLAGS

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.

mc/Makefile.am

@@ -1,12 +1,10 @@
 EXTRA_DIST = mc.h
 
-AM_CFLAGS = \
+AM_CPPFLAGS = \
   -DXRDP_CFG_PATH=\"${sysconfdir}/xrdp\" \
   -DXRDP_SBIN_PATH=\"${sbindir}\" \
   -DXRDP_SHARE_PATH=\"${datadir}/xrdp\" \
-  -DXRDP_PID_PATH=\"${localstatedir}/run\"
-
-INCLUDES = \
+  -DXRDP_PID_PATH=\"${localstatedir}/run\" \
   -I$(top_srcdir)/common
 
 lib_LTLIBRARIES = \