Add AsmPrinter support for emitting a directive to declare that
the code being generated does not require an executable stack.

Also, add target-specific code to make use of this on Linux
on x86. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50634 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/TargetAsmInfo.cpp b/lib/Target/TargetAsmInfo.cpp
index 2169945..c2504cc 100644
--- a/lib/Target/TargetAsmInfo.cpp
+++ b/lib/Target/TargetAsmInfo.cpp
@@ -26,6 +26,7 @@
   TLSDataSection("\t.section .tdata,\"awT\",@progbits"),
   TLSBSSSection("\t.section .tbss,\"awT\",@nobits"),
   ZeroFillDirective(0),
+  NonexecutableStackDirective(0),
   NeedsSet(false),
   MaxInstLength(4),
   PCSymbol("$"),