From f9bd60b7c0da8e9ad74ac5e20f0c7cb5cf690183 Mon Sep 17 00:00:00 2001
From: Stan Shebs <stanshebs@google.com>
Date: Mon, 24 Sep 2018 15:31:31 -0700
Subject: [PATCH] Add clang version of find_cxx_header

---
 configure    |  9 +++++++++
 configure.ac | 11 +++++++++++
 2 files changed, 20 insertions(+)

diff --git a/configure b/configure
index 0c64f966933..9591958b466 100755
--- a/configure
+++ b/configure
@@ -5365,10 +5365,19 @@ fi
 # Obtain some C++ header file paths.  This is used to make a local
 # copy of those headers in Makerules.
 if test -n "$CXX"; then
+  # In theory the clang and gcc regexes can be merged, but the
+  # result is incomprehensible.
+  if test "$with_clang" != no; then
+  find_cxx_header () {
+    echo "#include <$1>" | $CXX -M -MP -x c++ - 2>/dev/null \
+	 | sed -n "\,^[o.-]*[ :] /.*/$1 [\]$,{s,^[o.-]*[ :] /,/,;s/ [\]$//;p}"
+  }
+  else
   find_cxx_header () {
     echo "#include <$1>" | $CXX -M -MP -x c++ - 2>/dev/null \
 	 | sed -n "\,$1:,{s/:\$//;p}"
   }
+  fi
   CXX_CSTDLIB_HEADER="$(find_cxx_header cstdlib)"
   CXX_CMATH_HEADER="$(find_cxx_header cmath)"
   CXX_BITS_STD_ABS_H="$(find_cxx_header bits/std_abs.h)"
diff --git a/configure.ac b/configure.ac
index 9899b3d8483..cb6fb33ed94 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1067,15 +1067,26 @@ AC_SUBST(CXX_SYSINCLUDES)
 
 # Obtain some C++ header file paths.  This is used to make a local
 # copy of those headers in Makerules.
+changequote(,)dnl
 if test -n "$CXX"; then
+  # In theory the clang and gcc regexes can be merged, but the
+  # result is incomprehensible.
+  if test "$with_clang" != no; then
+  find_cxx_header () {
+    echo "#include <$1>" | $CXX -M -MP -x c++ - 2>/dev/null \
+	 | sed -n "\,^[o.-]*[ :] /.*/$1 [\]$,{s,^[o.-]*[ :] /,/,;s/ [\]$//;p}"
+  }
+  else
   find_cxx_header () {
     echo "#include <$1>" | $CXX -M -MP -x c++ - 2>/dev/null \
 	 | sed -n "\,$1:,{s/:\$//;p}"
   }
+  fi
   CXX_CSTDLIB_HEADER="$(find_cxx_header cstdlib)"
   CXX_CMATH_HEADER="$(find_cxx_header cmath)"
   CXX_BITS_STD_ABS_H="$(find_cxx_header bits/std_abs.h)"
 fi
+changequote([,])dnl
 AC_SUBST(CXX_CSTDLIB_HEADER)
 AC_SUBST(CXX_CMATH_HEADER)
 AC_SUBST(CXX_BITS_STD_ABS_H)
-- 
2.47.2