GUACAMOLE-249: Preserve CPPFLAGS such that modifications needed for FreeRDP tests affect only FreeRDP tests.

configure.ac

@@ -538,6 +538,10 @@ AC_ARG_WITH([rdp],
             [],
             [with_rdp=check])
 
+# Preserve CPPFLAGS so it can be restored later, following the addition of
+# options specific to FreeRDP tests
+OLDCPPFLAGS="$CPPFLAGS"
+
 if test "x$with_rdp" != "xno"
 then
     have_freerdp2=yes
@@ -657,6 +661,9 @@ then
 
 fi
 
+# Restore CPPFLAGS, removing FreeRDP-specific options needed for testing
+CPPFLAGS="$OLDCPPFLAGS"
+
 AM_CONDITIONAL([ENABLE_RDP], [test "x${have_freerdp2}" = "xyes"])
 
 #