[PATCH] configure.ac: fix include header discovery on gcc-12 [BZ #28183]

[Sergei Trofimovich via Libc-alpha <libc-alpha@sourceware.org>]

In https://gcc.gnu.org/PR101305 gcc introduced ABI-specific
internal `include` include directory:

gcc-12:
  /usr/lib/gcc/x86_64-pc-linux-gnu/12.0.0/32/include
  /usr/lib/gcc/x86_64-pc-linux-gnu/12.0.0/include
gcc-11:
  /usr/lib/gcc/x86_64-pc-linux-gnu/11.2.0/include

glibc's build system tries to extract only one of them and fails
the build for 32-bit ABI on x86_64:

  ../glibc/configure \
    --prefix=/usr \
    --build=x86_64-pc-linux-gnu \
    --host=i686-pc-linux-gnu \
    --with-headers=/usr/include \
    CC='x86_64-pc-linux-gnu-gcc -m32' \
    CXX='x86_64-pc-linux-gnu-g++ -m32' &&
  make

  python3 -B ../scripts/gen-as-const.py ...
  <stdin>:1:10: fatal error: stddef.h: No such file or directory

To workaround the failure we extend `configure.ac` to also
lookup `stddef.h` include directory and add it as a lower priority
search path.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
 configure    | 37 ++++++++++++++++++++++++++++++++++---
 configure.ac | 15 ++++++++++++---
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/configure b/configure
index 9619c10991..cac124f346 100755
--- a/configure
+++ b/configure
@@ -5452,15 +5452,46 @@ $as_echo "$as_me: WARNING:
 *** some features or tests will be disabled.
 *** Check the INSTALL file for required versions." >&2;}
 
-# if using special system headers, find out the compiler's sekrit
-# header directory and add that to the list.  NOTE: Only does the right
-# thing on a system that doesn't need fixincludes.  (Not presently a problem.)
+# If using special system headers, find out the compiler's internal
+# header directory and add that to the list to negate -nostdinc effect.
+# NOTE: Only does the right thing on a system that doesn't need fixincludes.
+# (Not presently a problem.)
+# NOTE: sometimes 'include' is also present in gcc's ABI-specific paths
+# like in https://sourceware.org/PR28183. To avoid it we probe a known
+# 'stddef.h' header that resides in a common include directory.
 if test -n "$sysheaders"; then
   SYSINCLUDES=-nostdinc
   for d in include include-fixed; do
     i=`$CC -print-file-name="$d"` && test "x$i" != x && test "x$i" != "x$d" &&
     SYSINCLUDES="$SYSINCLUDES -isystem $i"
   done
+  for f in include/stddef.h; do
+    i=`$CC -print-file-name="$f"` && test "x$i" != x && test "x$i" != "x$f" &&
+    d=`$as_dirname -- "$i" ||
+$as_expr X"$i" : 'X\(.*[^/]\)//*[^/][^/]*/*$' \| \
+	 X"$i" : 'X\(//\)[^/]' \| \
+	 X"$i" : 'X\(//\)$' \| \
+	 X"$i" : 'X\(/\)' \| . 2>/dev/null ||
+$as_echo X"$i" |
+    sed '/^X\(.*[^/]\)\/\/*[^/][^/]*\/*$/{
+	    s//\1/
+	    q
+	  }
+	  /^X\(\/\/\)[^/].*/{
+	    s//\1/
+	    q
+	  }
+	  /^X\(\/\/\)$/{
+	    s//\1/
+	    q
+	  }
+	  /^X\(\/\).*/{
+	    s//\1/
+	    q
+	  }
+	  s/.*/./; q'` &&
+    SYSINCLUDES="$SYSINCLUDES -isystem $d"
+  done
   SYSINCLUDES="$SYSINCLUDES \
 -isystem `echo $sysheaders | sed 's/:/ -isystem /g'`"
   if test -n "$CXX"; then
diff --git a/configure.ac b/configure.ac
index 34ecbba540..9507a552ff 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1083,15 +1083,24 @@ test -n "$aux_missing" && AC_MSG_WARN([
 *** some features or tests will be disabled.
 *** Check the INSTALL file for required versions.])
 
-# if using special system headers, find out the compiler's sekrit
-# header directory and add that to the list.  NOTE: Only does the right
-# thing on a system that doesn't need fixincludes.  (Not presently a problem.)
+# If using special system headers, find out the compiler's internal
+# header directory and add that to the list to negate -nostdinc effect.
+# NOTE: Only does the right thing on a system that doesn't need fixincludes.
+# (Not presently a problem.)
+# NOTE: sometimes 'include' is also present in gcc's ABI-specific paths
+# like in https://sourceware.org/PR28183. To avoid it we probe a known
+# 'stddef.h' header that resides in a common include directory.
 if test -n "$sysheaders"; then
   SYSINCLUDES=-nostdinc
   for d in include include-fixed; do
     i=`$CC -print-file-name="$d"` && test "x$i" != x && test "x$i" != "x$d" &&
     SYSINCLUDES="$SYSINCLUDES -isystem $i"
   done
+  for f in include/stddef.h; do
+    i=`$CC -print-file-name="$f"` && test "x$i" != x && test "x$i" != "x$f" &&
+    d=`AS_DIRNAME(["$i"])` &&
+    SYSINCLUDES="$SYSINCLUDES -isystem $d"
+  done
   SYSINCLUDES="$SYSINCLUDES \
 -isystem `echo $sysheaders | sed 's/:/ -isystem /g'`"
   if test -n "$CXX"; then
-- 
2.32.0