Issue #27453: CPP invocation in configure must use CPPFLAGS.

Patch by Chi Hsuan Yen.

Misc/ACKS

@@ -1663,3 +1663,4 @@ Gennadiy Zlobin
 Doug Zongker
 Peter Åstrand
 evilzero
+Chi Hsuan Yen

Misc/NEWS

@@ -145,6 +145,9 @@ Windows
 Build
 -----
 
+- Issue #27453: CPP invocation in configure must use CPPFLAGS. Patch by
+  Chi Hsuan Yen.
+
 - Issue #27490: Do not build pgen when cross-compiling.  Patch by Thomas
   Perl.
 

configure

@@ -5369,7 +5369,7 @@ cat >> conftest.c <<EOF
 
 EOF
 
-if $CPP conftest.c >conftest.out 2>/dev/null; then
+if $CPP $CPPFLAGS conftest.c >conftest.out 2>/dev/null; then
   PLATFORM_TRIPLET=`grep -v '^#' conftest.out | grep -v '^ *$' | tr -d ' 	'`
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: $PLATFORM_TRIPLET" >&5
 $as_echo "$PLATFORM_TRIPLET" >&6; }

configure.ac

@@ -870,7 +870,7 @@ cat >> conftest.c <<EOF
 
 EOF
 
-if $CPP conftest.c >conftest.out 2>/dev/null; then
+if $CPP $CPPFLAGS conftest.c >conftest.out 2>/dev/null; then
   PLATFORM_TRIPLET=`grep -v '^#' conftest.out | grep -v '^ *$' | tr -d ' 	'`
   AC_MSG_RESULT([$PLATFORM_TRIPLET])
 else