configure: Use check_cpp in CPP flags tests

configure

@@ -865,7 +865,7 @@ check_code(){
 
 check_cppflags(){
     log check_cppflags "$@"
-    check_cc "$@" <<EOF && append CPPFLAGS "$@"
+    check_cpp "$@" <<EOF && append CPPFLAGS "$@"
 int x;
 EOF
 }
@@ -1135,7 +1135,7 @@ check_host_cpp(){
 
 check_host_cppflags(){
     log check_host_cppflags "$@"
-    check_host_cc "$@" <<EOF && append host_cppflags "$@"
+    check_host_cpp "$@" <<EOF && append host_cppflags "$@"
 int x;
 EOF
 }