From 596183a1eed0699be96bdcd495ab1b497370afda Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Wed, 2 Nov 2022 11:55:57 -0300
Subject: Rewrite find_cxx_header config configure.ac

With clang if the main file is <stdin>, the first non-main-file
dependency is not listed in the -MP output.  Although it was fixed
on clang-16 [1], this change adds portability for older version.

[1] https://github.com/llvm/llvm-project/commit/ff9576f74514b836e1ba0268409a2ecb919d7118

Reviewed-by: Fangrui Song <maskray@google.com>
---
 configure.ac | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index 9fc1fb1c1c..20b5e8043f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1137,8 +1137,8 @@ AC_SUBST(CXX_SYSINCLUDES)
 # copy of those headers in Makerules.
 if test -n "$CXX"; then
   find_cxx_header () {
-    echo "#include <$1>" | $CXX -M -MP -x c++ - 2>/dev/null \
-	 | sed -n "\,$1:,{s/:\$//;p}"
+    echo "#include <$1>" | $CXX -H -fsyntax-only -x c++ - 2>&1 \
+	 | $AWK '$1 == "."{print $2}'
   }
   CXX_CSTDLIB_HEADER="$(find_cxx_header cstdlib)"
   CXX_CMATH_HEADER="$(find_cxx_header cmath)"
-- 
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