Fix wrong configure test for abi::__forced_unwind in previous commit.

The previous commit was accidental and contained an initial version of the
patch which didn't test for NPTL abi::__forced_unwind correctly and just
tested whether cxxabi.h header was available.

Tighten the check to work on the other systems and check for __forced_unwind
existence itself.

Also check for cxxabi.h before testing for __cxa_demangle as there is no need
to try to compile another test program if we already know that this entire
header is unavailable anyhow.

See #14626.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72532 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/threadpsx.cpp

@@ -54,7 +54,7 @@
     #include <thread.h>
 #endif
 
-#ifdef HAVE_CXXABI_H
+#ifdef HAVE_ABI_FORCEDUNWIND
     #include <cxxabi.h>
 #endif
 
@@ -861,7 +861,7 @@ void *wxThreadInternal::PthreadStart(wxThread *thread)
                        wxT("Thread %p Entry() returned %lu."),
                        THR_ID(pthread), wxPtrToUInt(pthread->m_exitcode));
         }
-#ifdef HAVE_CXXABI_H
+#ifdef HAVE_ABI_FORCEDUNWIND
         // When using common C++ ABI under Linux we must always rethrow this
         // special exception used to unwind the stack when the thread was
         // cancelled, otherwise the thread library would simply terminate the
@@ -872,7 +872,7 @@ void *wxThreadInternal::PthreadStart(wxThread *thread)
             pthread->SetState(STATE_EXITED);
             throw;
         }
-#endif // HAVE_CXXABI_H
+#endif // HAVE_ABI_FORCEDUNWIND
         wxCATCH_ALL( wxTheApp->OnUnhandledException(); )
 
         {