wrappers: Handle tools named [<target>-]llvm-<tool>

Normally, we'd split the string at the last dash. However if the
tool name is "llvm-<tool>", make sure to include "llvm-" in the
tool name part when splitting the executable name.

In llvm-wrapper, don't add a duplicate "llvm-" prefix for the tool
name in these cases.

wrappers/native-wrapper.h

@@ -154,6 +154,21 @@ static inline void split_argv(const TCHAR *argv0, const TCHAR **dir_ptr, const T
     if (dash) {
         *dash = '\0';
         exe = dash + 1;
+        // Handle [<target>-]llvm-<tool> as exe=llvm-<tool>
+        TCHAR *dash2 = _tcsrchr(target, '-');
+        if (dash2 && !_tcscmp(dash2, _T("-llvm"))) {
+            // Found <target>-llvm-<tool>; move the llvm- prefix to
+            // exe. Convert the original dash which we overwrite with '\0'
+            // back into a dash and split the string at the preceding dash.
+            *dash = '-';
+            *dash2 = '\0';
+            exe = dash2 + 1;
+        } else if (!_tcscmp(target, _T("llvm"))) {
+            // Found llvm-<tool>; don't treat "llvm" as target but move
+            // it to the exe part.
+            exe = basename;
+            target = NULL;
+        }
     } else {
         target = NULL;
     }