Teach the driver on Linux to respect -nodefaultlibs.

Patch from Andrew C. Morrow.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156771 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 769bd81..e396669 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -5313,7 +5313,9 @@
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs);
 
-  if (D.CCCIsCXX && !Args.hasArg(options::OPT_nostdlib)) {
+  if (D.CCCIsCXX &&
+      !Args.hasArg(options::OPT_nostdlib) &&
+      !Args.hasArg(options::OPT_nodefaultlibs)) {
     bool OnlyLibstdcxxStatic = Args.hasArg(options::OPT_static_libstdcxx) &&
       !Args.hasArg(options::OPT_static);
     if (OnlyLibstdcxxStatic)
@@ -5328,22 +5330,23 @@
   addAsanRTLinux(getToolChain(), Args, CmdArgs);
 
   if (!Args.hasArg(options::OPT_nostdlib)) {
-    if (Args.hasArg(options::OPT_static))
-      CmdArgs.push_back("--start-group");
+    if (!Args.hasArg(options::OPT_nodefaultlibs)) {
+      if (Args.hasArg(options::OPT_static))
+        CmdArgs.push_back("--start-group");
 
-    AddLibgcc(ToolChain.getTriple(), D, CmdArgs, Args);
-
-    if (Args.hasArg(options::OPT_pthread) ||
-        Args.hasArg(options::OPT_pthreads))
-      CmdArgs.push_back("-lpthread");
-
-    CmdArgs.push_back("-lc");
-
-    if (Args.hasArg(options::OPT_static))
-      CmdArgs.push_back("--end-group");
-    else
       AddLibgcc(ToolChain.getTriple(), D, CmdArgs, Args);
 
+      if (Args.hasArg(options::OPT_pthread) ||
+          Args.hasArg(options::OPT_pthreads))
+        CmdArgs.push_back("-lpthread");
+
+      CmdArgs.push_back("-lc");
+
+      if (Args.hasArg(options::OPT_static))
+        CmdArgs.push_back("--end-group");
+      else
+        AddLibgcc(ToolChain.getTriple(), D, CmdArgs, Args);
+    }
 
     if (!Args.hasArg(options::OPT_nostartfiles)) {
       const char *crtend;
diff --git a/test/Driver/nodefaultlib.c b/test/Driver/nodefaultlib.c
new file mode 100644
index 0000000..518928a
--- /dev/null
+++ b/test/Driver/nodefaultlib.c
@@ -0,0 +1,8 @@
+// RUN: %clang -target i686-pc-linux-gnu -### -nodefaultlibs %s 2> %t
+// RUN: FileCheck < %t %s
+//
+// CHECK-NOT: start-group
+// CHECK-NOT: -lgcc
+// CHECK-NOT: -lc
+// CHECK: crtbegin
+// CHECK: crtend