From e367d65b6e5110b196f90a58750d423d60daa446 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Wed, 1 Nov 2017 20:59:34 +0200
Subject: [PATCH] Fix use of _alloca under g++/clang (mingw/cygwin)

---
 include/boost/system/detail/error_code.ipp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/boost/system/detail/error_code.ipp b/include/boost/system/detail/error_code.ipp
index a7fe3ef..a2b3f11 100644
--- a/include/boost/system/detail/error_code.ipp
+++ b/include/boost/system/detail/error_code.ipp
@@ -411,8 +411,14 @@ namespace
     }
     
     int num_chars = (buf.size() + 1) * 2;
+
     boost::winapi::LPSTR_ narrow_buffer =
+#if defined(__GNUC__)
+      (boost::winapi::LPSTR_)__builtin_alloca(num_chars);
+#else
       (boost::winapi::LPSTR_)_alloca(num_chars);
+#endif
+
     if (boost::winapi::WideCharToMultiByte(boost::winapi::CP_ACP_, 0,
       buf.c_str(), -1, narrow_buffer, num_chars, NULL, NULL) == 0)
     {