Fix build (failure was noted in #147) (#151)

build/Jamfile.v2

@@ -138,6 +138,10 @@ lib boost_stacktrace_from_exception
   : # requirements
     <warnings>all
     <target-os>linux:<library>dl
+    <target-os>windows:<build>no  # not supported at the moment
+
+    # Require usable libbacktrace on other platforms
+    [ check-target-builds ../build//libbacktrace : : <build>no ]
   : # default build
   : # usage-requirements
     #<link>shared:<define>BOOST_STACKTRACE_DYN_LINK=1

doc/stacktrace.qbk

@@ -133,8 +133,8 @@ Generic recommendation is to *avoid signal handlers! Use* platform specific ways
 [section Stacktrace from arbitrary exception]
 
 [warning At the moment the functionality is only available for some of the
-         popular cxx run-times for POSIX systems. Make sure that your platform
-         is supported by running some tests.
+         popular C++ runtimes for POSIX systems and requires *libbacktrace*.
+         Make sure that your platform is supported by running some tests.
 ]
 
 The library provides a way to get stacktrace from an exception as if the

src/from_exception.cpp

@@ -6,6 +6,12 @@
 
 #include "exception_headers.h"
 
+// At the moment the file is used only on POSIX. _Unwind_Backtrace may be
+// available on some platforms only if _GNU_SOURCE is defined.
+#ifndef _GNU_SOURCE
+#   define _GNU_SOURCE
+#endif
+
 #include <boost/assert.hpp>
 #include <boost/stacktrace/safe_dump_to.hpp>