Long live the exception handling!

This patch fills the last necessary bits to enable exceptions
handling in LLVM. Currently only on x86-32/linux.

In fact, this patch adds necessary intrinsics (and their lowering) which
represent really weird target-specific gcc builtins used inside unwinder.

After corresponding llvm-gcc patch will land (easy) exceptions should be
more or less workable. However, exceptions handling support should not be 
thought as 'finished': I expect many small and not so small glitches
everywhere.

llvm-svn: 39855
diff --git a/llvm/lib/Target/X86/X86TargetAsmInfo.cpp b/llvm/lib/Target/X86/X86TargetAsmInfo.cpp
index dbf202c..4bb854e 100644
--- a/llvm/lib/Target/X86/X86TargetAsmInfo.cpp
+++ b/llvm/lib/Target/X86/X86TargetAsmInfo.cpp
@@ -124,8 +124,9 @@
     DwarfARangesSection = "\t.section\t.debug_aranges,\"\",@progbits";
     DwarfRangesSection =  "\t.section\t.debug_ranges,\"\",@progbits";
     DwarfMacInfoSection = "\t.section\t.debug_macinfo,\"\",@progbits";
-    
-    SupportsExceptionHandling = true;
+
+    if (!Subtarget->is64Bit())
+      SupportsExceptionHandling = true;
     DwarfEHFrameSection = "\t.section\t.eh_frame,\"aw\",@progbits";
     DwarfExceptionSection = "\t.section\t.gcc_except_table,\"a\",@progbits";
     break;