Use LLVM-style command line (instead of DMD-style)

Note: For a backward compatible interface, use the new bin/ldmd script. It
      supports all old options while passing on anything it doesn't recognize.

Some changes caused by this:
* -debug and -version are now -d-debug and -d-version due to a conflict with
  standard LLVM options.
* All "flag" options now allow an optional =true/=1/=false/=0 suffix.
* Some "hidden debug switches" starting with "--" were renamed because LLVM
  doesn't care about the number of dashes, so they were conflicting with other
  options (such as -c).
  The new versions start with "-hidden-debug-" instead of "--"
* --help works, but has a non-zero exit code. This breaks some Tango scripts
  which use it to test for compiler existence. See tango.patch.

Some changes not (directly) caused by this;
* (-enable/-disable)-FOO options are now available for pre- and postconditions.
* -march is used instead of -m (like other LLVM programs), but -m is an alias
  for it.
* -defaultlib, -debuglib, -d-debug and -d-version allow comma-separated values.
  The effect should be identical to specifying the same option multiple times.
  I decided against allowing these for some other options because paths might
  contain commas on some systems.
* -fPIC is removed in favor of the standard LLVM option -relocation-model=pic

Bug:
* If -run is specified as the last argument in DFLAGS, no error is generated.
  (Not very serious IMHO)

gen/runtime.cpp

@@ -2,6 +2,7 @@
 #include "llvm/Module.h"
 #include "llvm/Bitcode/ReaderWriter.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/CommandLine.h"
 
 #include "root.h"
 #include "mars.h"
@@ -15,6 +16,14 @@
 #include "gen/tollvm.h"
 #include "gen/irstate.h"
 
+//////////////////////////////////////////////////////////////////////////////////////////////////
+
+static llvm::cl::opt<bool> noruntime("noruntime",
+    llvm::cl::desc("Do not allow code that generates implicit runtime calls"),
+    llvm::cl::ZeroOrMore);
+
+//////////////////////////////////////////////////////////////////////////////////////////////////
+
 static llvm::Module* M = NULL;
 static bool runtime_failed = false;
 
@@ -44,7 +53,7 @@ void LLVM_D_FreeRuntime()
 
 llvm::Function* LLVM_D_GetRuntimeFunction(llvm::Module* target, const char* name)
 {
-    if (global.params.noruntime) {
+    if (noruntime) {
         error("No implicit runtime calls allowed with -noruntime option enabled");
         fatal();
     }
@@ -80,7 +89,7 @@ llvm::GlobalVariable* LLVM_D_GetRuntimeGlobal(llvm::Module* target, const char*
         return gv;
     }
 
-    if (global.params.noruntime) {
+    if (noruntime) {
         error("No implicit runtime calls allowed with -noruntime option enabled");
         fatal();
     }