From fefd3d2dccbd21b01a649fa9683d98f2648c83f6 Mon Sep 17 00:00:00 2001
From: Dustin Spicuzza <dustin@virtualroadside.com>
Date: Sat, 3 Oct 2020 12:31:44 -0400
Subject: [PATCH] bpo-41916: allow cross-compiled python to have -pthread set
 for CXX

When cross-compiling, the compile/run test for -pthread always fails so -pthread
will never be automatically set without an override from the cache. ac_cv_pthread
can already be overridden, so do the same thing for ac_cv_cxx_thread.
---
 .../Build/2022-03-04-10-47-23.bpo-41916.1d2GLU.rst  |  2 ++
 configure                                           | 13 ++++++++++---
 configure.ac                                        | 12 +++++++-----
 3 files changed, 19 insertions(+), 8 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Build/2022-03-04-10-47-23.bpo-41916.1d2GLU.rst

diff --git a/Misc/NEWS.d/next/Build/2022-03-04-10-47-23.bpo-41916.1d2GLU.rst b/Misc/NEWS.d/next/Build/2022-03-04-10-47-23.bpo-41916.1d2GLU.rst
new file mode 100644
index 00000000000000..2fc5f8ec77b132
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2022-03-04-10-47-23.bpo-41916.1d2GLU.rst
@@ -0,0 +1,2 @@
+Allow override of ac_cv_cxx_thread so that cross compiled python can set
+-pthread for CXX.
diff --git a/configure b/configure
index 0e9f72faa7b120..72886b2a9522c4 100755
--- a/configure
+++ b/configure
@@ -9509,12 +9509,14 @@ fi
 
 # If we have set a CC compiler flag for thread support then
 # check if it works for CXX, too.
-ac_cv_cxx_thread=no
 if test ! -z "$CXX"
 then
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CXX also accepts flags for thread support" >&5
 $as_echo_n "checking whether $CXX also accepts flags for thread support... " >&6; }
-ac_save_cxx="$CXX"
+if ${ac_cv_cxx_thread+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_save_cxx="$CXX"
 
 if test "$ac_cv_kpthread" = "yes"
 then
@@ -9528,6 +9530,8 @@ elif test "$ac_cv_pthread" = "yes"
 then
   CXX="$CXX -pthread"
   ac_cv_cxx_thread=yes
+else
+  ac_cv_cxx_thread=no
 fi
 
 if test $ac_cv_cxx_thread = yes
@@ -9543,10 +9547,13 @@ then
   fi
   rm -fr conftest*
 fi
+CXX="$ac_save_cxx"
+fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_cxx_thread" >&5
 $as_echo "$ac_cv_cxx_thread" >&6; }
+else
+  ac_cv_cxx_thread=no
 fi
-CXX="$ac_save_cxx"
 
 
 
diff --git a/configure.ac b/configure.ac
index a4f3b0ab84664a..7fcf7949c1e163 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2664,11 +2664,10 @@ fi
 
 # If we have set a CC compiler flag for thread support then
 # check if it works for CXX, too.
-ac_cv_cxx_thread=no
 if test ! -z "$CXX"
 then
-AC_MSG_CHECKING(whether $CXX also accepts flags for thread support)
-ac_save_cxx="$CXX"
+AC_CACHE_CHECK([whether $CXX also accepts flags for thread support], [ac_cv_cxx_thread],
+[ac_save_cxx="$CXX"
 
 if test "$ac_cv_kpthread" = "yes"
 then
@@ -2682,6 +2681,8 @@ elif test "$ac_cv_pthread" = "yes"
 then
   CXX="$CXX -pthread"
   ac_cv_cxx_thread=yes
+else
+  ac_cv_cxx_thread=no
 fi
 
 if test $ac_cv_cxx_thread = yes
@@ -2697,9 +2698,10 @@ then
   fi
   rm -fr conftest*
 fi
-AC_MSG_RESULT($ac_cv_cxx_thread)
+CXX="$ac_save_cxx"])
+else
+  ac_cv_cxx_thread=no
 fi
-CXX="$ac_save_cxx"
 
 dnl # check for ANSI or K&R ("traditional") preprocessor
 dnl AC_MSG_CHECKING(for C preprocessor type)