[PATCH v2 2/4] Rewrite find_cxx_header config configure.ac

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

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
---
 configure    | 4 ++--
 configure.ac | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/configure b/configure
index fc3d7842de..e23ea95a49 100755
--- a/configure
+++ b/configure
@@ -5669,8 +5669,8 @@ fi
 # 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="$(find_cxx_header cmath)"
diff --git a/configure.ac b/configure.ac
index 9fc1fb1c1c..7275b53345 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1137,8 +1137,8 @@ AC_SUBST(CXX_SYSINCLUDES)
 # copy of those headers in Makerules.
 if test -n "$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)"
-- 
2.34.1