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/cl_helpers.cpp

@@ -0,0 +1,81 @@
+#include "gen/cl_helpers.h"
+
+#include "dmd/root.h"
+#include "dmd/mem.h"
+
+#include <cctype>       // isupper, tolower
+#include <algorithm>
+#include <utility>
+#include <stdarg.h>
+
+namespace opts {
+
+// Helper function
+static char toLower(char c) {
+    if (isupper(c))
+        return tolower(c);
+    return c;
+}
+
+bool FlagParser::parse(cl::Option &O, const char *ArgName, const std::string &Arg, bool &Val) {
+    // Make a std::string out of it to make comparisons easier
+    // (and avoid repeated conversion)
+    std::string argname = ArgName;
+    
+    typedef std::vector<std::pair<std::string, bool> >::iterator It;
+    for (It I = switches.begin(), E = switches.end(); I != E; ++I) {
+        std::string name = I->first;
+        if (name == argname
+                || (name.length() < argname.length()
+                    && argname.substr(0, name.length()) == name
+                    && argname[name.length()] == '=')) {
+            
+            if (!cl::parser<bool>::parse(O, ArgName, Arg, Val)) {
+                Val = (Val == I->second);
+                return false;
+            }
+            // Invalid option value
+            break;
+        }
+    }
+    return true;
+}
+
+void FlagParser::getExtraOptionNames(std::vector<const char*> &Names) {
+    typedef std::vector<std::pair<std::string, bool> >::iterator It;
+    for (It I = switches.begin() + 1, E = switches.end(); I != E; ++I) {
+        Names.push_back(I->first.c_str());
+    }
+}
+
+
+MultiSetter::MultiSetter(bool invert, bool* p, ...) {
+    this->invert = invert;
+    if (p) {
+        locations.push_back(p);
+        va_list va;
+        va_start(va, p);
+        while (p = va_arg(va, bool*)) {
+            locations.push_back(p);
+        }
+    }
+}
+        
+void MultiSetter::operator=(bool val) {
+    typedef std::vector<bool*>::iterator It;
+    for (It I = locations.begin(), E = locations.end(); I != E; ++I) {
+        **I = (val != invert);
+    }
+}
+
+
+void ArrayAdapter::push_back(const char* cstr) {
+    if (!cstr || !*cstr)
+        error("Expected argument to '-%s'", name);
+    
+    if (!*arrp)
+        *arrp = new Array;
+    (*arrp)->push(mem.strdup(cstr));
+}
+
+} // namespace opts