clang: Add support for a CC_PRINT_HEADERS environment variable, which mirrors
CC_PRINT_OPTIONS and can be used to get some out-of-band information on header
usage from a build.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124751 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Driver.cpp b/lib/Driver/Driver.cpp
index df32eb3..d56b1d2 100644
--- a/lib/Driver/Driver.cpp
+++ b/lib/Driver/Driver.cpp
@@ -58,8 +58,9 @@
     DefaultImageName(_DefaultImageName),
     DriverTitle("clang \"gcc-compatible\" driver"),
     Host(0),
-    CCPrintOptionsFilename(0), CCCIsCXX(false),
-    CCCEcho(false), CCCPrintBindings(false), CCPrintOptions(false), CCCGenericGCCName("gcc"),
+    CCPrintOptionsFilename(0), CCPrintHeadersFilename(0), CCCIsCXX(false),
+    CCCEcho(false), CCCPrintBindings(false), CCPrintOptions(false),
+    CCPrintHeaders(false), CCCGenericGCCName("gcc"),
     CheckInputsExist(true), CCCUseClang(true), CCCUseClangCXX(true),
     CCCUseClangCPP(true), CCCUsePCH(true), SuppressMissingInputWarning(false) {
   if (IsProduction) {