From 6184f4153fce2e77898c9a9c0f316ac19490fd6b Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Wed, 21 Sep 2016 10:45:32 +0200
Subject: Avoid running $(CXX) during build to obtain header file paths

This reduces the build time somewhat and is particularly noticeable
during rebuilds with few code changes.

(cherry picked from commit fc3e1337be1c6935ab58bd13520f97a535cf70cc)
---
 configure.ac | 12 ++++++++++++
 1 file changed, 12 insertions(+)

(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index 8277d9f..1905e93 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1039,6 +1039,18 @@ fi
 AC_SUBST(SYSINCLUDES)
 AC_SUBST(CXX_SYSINCLUDES)
 
+# Obtain some C++ header file paths.  This is used to make a local
+# copy of those headers in Makerules.
+if test -n "$CXX"; then
+  find_cxx_header () {
+    echo "#include <$1>" | $CXX -M -MP -x c++ - | sed -n "/$1:/{s/:\$//;p}"
+  }
+  CXX_CSTDLIB_HEADER="$(find_cxx_header cstdlib)"
+  CXX_CMATH_HEADER="$(find_cxx_header cmath)"
+fi
+AC_SUBST(CXX_CSTDLIB_HEADER)
+AC_SUBST(CXX_CMATH_HEADER)
+
 # Test if LD_LIBRARY_PATH contains the notation for the current directory
 # since this would lead to problems installing/building glibc.
 # LD_LIBRARY_PATH contains the current directory if one of the following
-- 
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