[Frontend] Fix an issue where a quoted search path is incorrectly removed as a duplicate header search path

[arphaman]

Summary

The commit r126167 started passing the First index into RemoveDuplicates, but forgot to update 0 to First in the loop that looks for the duplicate. This resulted in a bug where an -iquoted search path was incorrectly removed if you passed in the same path into -iquote and more than one time into -isystem.

[mehdi_amini]

LGTM.

[bruno]

LGTM!

cfe/trunk/lib/Frontend/InitHeaderSearch.cpp

for (unsigned i = First; i != SearchList.size(); ++i) {
     // ignore the user's request and drop the user dir... keeping the system
     // dir.  This is weird, but required to emulate GCC's search path correctly.
     //
     // Since dupes of system dirs are rare, just rescan to find the original
     // that we're nuking instead of using a DenseMap.
     if (CurEntry.getDirCharacteristic() != SrcMgr::C_User) {
       // Find the dir that this is the same of.
       unsigned FirstDir;
-      for (FirstDir = 0; ; ++FirstDir) {
+      for (FirstDir = First;; ++FirstDir) {
         assert(FirstDir != i && "Didn't find dupe?");
 
         const DirectoryLookup &SearchEntry = SearchList[FirstDir];
 
         // If these are different lookup types, then they can't be the dupe.
         if (SearchEntry.getLookupType() != CurEntry.getLookupType())
           continue;
 

cfe/trunk/test/Frontend/include-duplicate-removal.c

+// RUN: %clang_cc1 -v -I%S/Inputs -iquote %S/Inputs/SystemHeaderPrefix -isystem %S/Inputs/SystemHeaderPrefix -isystem %S/Inputs/SystemHeaderPrefix %s 2>&1 | FileCheck %s
+
+#include <test.h>
+
+// CHECK: ignoring duplicate directory
+// CHECK-SAME: Inputs/SystemHeaderPrefix"{{$}}
+
+// CHECK:      #include "..."
+// CHECK-NEXT: {{.*}}Inputs/SystemHeaderPrefix{{$}}
+// CHECK-NEXT: #include <...>
+// CHECK-NEXT: {{.*}}Inputs{{$}}
+// CHECK-NEXT: {{.*}}Inputs/SystemHeaderPrefix{{$}}