Merge EXTRA_DEFINES and EXTRA_INCLUDES into AM_CPPFLAGS

AM_CPPFLAGS is a documented Automake variable for C preprocessor flags
that should not be overridden when compiling the package.

There is no need to have two additional variables that are ultimately
merged into AM_CPPFLAGS.

Their names are also confusing. EXTDA_DIST is a documented Automake
variable. Everything else that starts with "EXTRA" is not.

neutrinordp/Makefile.am

@@ -1,20 +1,17 @@
-EXTRA_DEFINES =
- 
-if XRDP_DEBUG
-EXTRA_DEFINES += -DXRDP_DEBUG
-else
-EXTRA_DEFINES += -DXRDP_NODEBUG
-endif
-
 AM_CPPFLAGS = \
   -DXRDP_CFG_PATH=\"${sysconfdir}/xrdp\" \
   -DXRDP_SBIN_PATH=\"${sbindir}\" \
   -DXRDP_SHARE_PATH=\"${datadir}/xrdp\" \
   -DXRDP_PID_PATH=\"${localstatedir}/run\" \
-  $(EXTRA_DEFINES) \
   -I$(top_srcdir)/common \
   $(FREERDP_CFLAGS)
 
+if XRDP_DEBUG
+AM_CPPFLAGS += -DXRDP_DEBUG
+else
+AM_CPPFLAGS += -DXRDP_NODEBUG
+endif
+
 module_LTLIBRARIES = \
   libxrdpneutrinordp.la