[llvm] gn build: libcxx: Select the std_thread pstl backend. (PR #132455)

[Peter Collingbourne via llvm-commits]

https://github.com/pcc created https://github.com/llvm/llvm-project/pull/132455

In the CMake build the default pstl backend for libc++ when threads are
enabled is std_thread. By selecting the wrong backend we were triggering
some transitive_includes test failures.


>From f2207e1df60cec950dbab391fec90a5895389cce Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <pcc at google.com>
Date: Fri, 21 Mar 2025 12:08:06 -0700
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.6-beta.1
---
 llvm/utils/gn/secondary/libcxx/include/BUILD.gn | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/utils/gn/secondary/libcxx/include/BUILD.gn b/llvm/utils/gn/secondary/libcxx/include/BUILD.gn
index e59320477ffe4..8a25bb9c60fcf 100644
--- a/llvm/utils/gn/secondary/libcxx/include/BUILD.gn
+++ b/llvm/utils/gn/secondary/libcxx/include/BUILD.gn
@@ -41,8 +41,8 @@ if (current_toolchain == default_toolchain) {
       "_LIBCPP_ABI_DEFINES=",
       "_LIBCPP_HARDENING_MODE_DEFAULT=_LIBCPP_HARDENING_MODE_NONE",
       "_LIBCPP_PSTL_BACKEND_LIBDISPATCH=",
-      "_LIBCPP_PSTL_BACKEND_SERIAL=1",
-      "_LIBCPP_PSTL_BACKEND_STD_THREAD=",
+      "_LIBCPP_PSTL_BACKEND_SERIAL=",
+      "_LIBCPP_PSTL_BACKEND_STD_THREAD=1",
     ]
     if (libcxx_abi_namespace != "") {
       values += [ "_LIBCPP_ABI_NAMESPACE=$libcxx_abi_namespace" ]