Added -disable-red-zone flag.

This will disable the usage of the 'red-zone' in ABIs that make use of it (like x86). This mimics the exact flag used by clang. It is comparable to the -mno-red-zone flag in gcc. - thanks to wilkie

gen/cl_options.cpp

@@ -100,6 +100,10 @@ cl::opt<bool> output_s("output-s",
 cl::opt<cl::boolOrDefault> output_o("output-o",
     cl::desc("Write native object"));
 
+// Disabling Red Zone
+cl::opt<bool> disableRedZone("disable-red-zone",
+  cl::desc("Do not emit code that uses the red zone."),
+  cl::init(false));
 
 // DDoc options
 static cl::opt<bool, true> doDdoc("D",

gen/cl_options.h

@@ -26,6 +26,7 @@ namespace opts {
     extern cl::opt<bool> output_ll;
     extern cl::opt<bool> output_s;
     extern cl::opt<cl::boolOrDefault> output_o;
+    extern cl::opt<bool> disableRedZone;
     extern cl::opt<std::string> ddocDir;
     extern cl::opt<std::string> ddocFile;
     extern cl::opt<std::string> jsonFile;

gen/functions.cpp

@@ -22,6 +22,7 @@
 #include "gen/dvalue.h"
 #include "gen/abi.h"
 #include "gen/nested.h"
+#include "gen/cl_options.h"
 
 using namespace llvm::Attribute;
 
@@ -501,6 +502,9 @@ void DtoDeclareFunction(FuncDeclaration* fdecl)
     // parameter attributes
     if (!fdecl->isIntrinsic()) {
         set_param_attrs(f, func, fdecl);
+        if (opts::disableRedZone) {
+            func->addFnAttr(NoRedZone);
+        }
     }
 
     // main