diff --git a/Makefile.config.in b/Makefile.config.in
index fff482e7774..9755a5de078 100644
--- a/Makefile.config.in
+++ b/Makefile.config.in
@@ -46,11 +46,19 @@ realpath = $(shell cd $(1); $(PWD))
 PROJ_OBJ_DIR  := $(call realpath, .)
 PROJ_OBJ_ROOT := $(call realpath, $(PROJ_OBJ_DIR)/$(LEVEL))
 
+CLANG_SRC_ROOT  := @CLANG_SRC_ROOT@
+
 ifeq ($(PROJECT_NAME),llvm)
 LLVM_SRC_ROOT   := $(call realpath, @abs_top_srcdir@)
 LLVM_OBJ_ROOT   := $(call realpath, @abs_top_builddir@)
 PROJ_SRC_ROOT   := $(LLVM_SRC_ROOT)
-PROJ_SRC_DIR    := $(call realpath, $(LLVM_SRC_ROOT)/$(patsubst $(PROJ_OBJ_ROOT)%,%,$(PROJ_OBJ_DIR)))
+PROJ_SRC_DIR    := $(LLVM_SRC_ROOT)$(patsubst $(PROJ_OBJ_ROOT)%,%,$(PROJ_OBJ_DIR))
+
+ifneq ($(CLANG_SRC_ROOT),)
+  CLANG_SRC_ROOT:= $(call realpath, $(CLANG_SRC_ROOT))
+  PROJ_SRC_DIR  := $(patsubst $(LLVM_SRC_ROOT)/tools/clang%,$(CLANG_SRC_ROOT)%,$(PROJ_SRC_DIR))
+endif
+
 prefix          := @prefix@
 PROJ_prefix     := $(prefix)
 PROJ_VERSION    := $(LLVMVersion)
diff --git a/autoconf/configure.ac b/autoconf/configure.ac
index 128dd7f9786..b8b61bc16b4 100644
--- a/autoconf/configure.ac
+++ b/autoconf/configure.ac
@@ -795,6 +795,17 @@ case "$withval" in
   *) AC_MSG_ERROR([Invalid path for --with-ocaml-libdir. Provide full path]) ;;
 esac
 
+AC_ARG_WITH(clang-srcdir,
+  AS_HELP_STRING([--with-clang-srcdir],
+    [Directory to the out-of-tree Clang source]),,
+    withval="-")
+case "$withval" in
+  -) clang_src_root="" ;;
+  /* | [[A-Za-z]]:[[\\/]]*) clang_src_root="$withval" ;;
+  *) clang_src_root="$ac_pwd/$withval" ;;
+esac
+AC_SUBST(CLANG_SRC_ROOT,[$clang_src_root])
+
 AC_ARG_WITH(clang-resource-dir,
   AS_HELP_STRING([--with-clang-resource-dir],
     [Relative directory from the Clang binary for resource files]),,
diff --git a/configure b/configure
index 49e189a4696..c8b3c767ad0 100755
--- a/configure
+++ b/configure
@@ -708,6 +708,7 @@ ENABLE_CBE_PRINTF_A
 OPTIMIZE_OPTION
 EXTRA_OPTIONS
 EXTRA_LD_OPTIONS
+CLANG_SRC_ROOT
 BINUTILS_INCDIR
 NM
 ifGNUmake
@@ -1433,6 +1434,7 @@ Optional Packages:
   --with-extra-ld-options Specify additional options to link LLVM with
   --with-ocaml-libdir     Specify install location for ocaml bindings (default
                           is stdlib)
+  --with-clang-srcdir     Directory to the out-of-tree Clang source
   --with-clang-resource-dir
                           Relative directory from the Clang binary for
                           resource files
@@ -5510,6 +5512,22 @@ echo "$as_me: error: Invalid path for --with-ocaml-libdir. Provide full path" >&
 esac
 
 
+# Check whether --with-clang-srcdir was given.
+if test "${with_clang_srcdir+set}" = set; then
+  withval=$with_clang_srcdir;
+else
+  withval="-"
+fi
+
+case "$withval" in
+  -) clang_src_root="" ;;
+  /* | [A-Za-z]:[\\/]*) clang_src_root="$withval" ;;
+  *) clang_src_root="$ac_pwd/$withval" ;;
+esac
+CLANG_SRC_ROOT=$clang_src_root
+
+
+
 # Check whether --with-clang-resource-dir was given.
 if test "${with_clang_resource_dir+set}" = set; then
   withval=$with_clang_resource_dir;
@@ -10453,7 +10471,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<EOF
-#line 10456 "configure"
+#line 10474 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -21906,6 +21924,7 @@ ENABLE_CBE_PRINTF_A!$ENABLE_CBE_PRINTF_A$ac_delim
 OPTIMIZE_OPTION!$OPTIMIZE_OPTION$ac_delim
 EXTRA_OPTIONS!$EXTRA_OPTIONS$ac_delim
 EXTRA_LD_OPTIONS!$EXTRA_LD_OPTIONS$ac_delim
+CLANG_SRC_ROOT!$CLANG_SRC_ROOT$ac_delim
 BINUTILS_INCDIR!$BINUTILS_INCDIR$ac_delim
 NM!$NM$ac_delim
 ifGNUmake!$ifGNUmake$ac_delim
@@ -21987,7 +22006,7 @@ LIBOBJS!$LIBOBJS$ac_delim
 LTLIBOBJS!$LTLIBOBJS$ac_delim
 _ACEOF
 
-  if test `sed -n "s/.*$ac_delim\$/X/p" conf$$subs.sed | grep -c X` = 88; then
+  if test `sed -n "s/.*$ac_delim\$/X/p" conf$$subs.sed | grep -c X` = 89; then
     break
   elif $ac_last_try; then
     { { echo "$as_me:$LINENO: error: could not make $CONFIG_STATUS" >&5
diff --git a/tools/Makefile b/tools/Makefile
index 68ce314c92a..2da39177815 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -9,8 +9,15 @@
 
 LEVEL := ..
 
+include $(LEVEL)/Makefile.config
+
 # Build clang if present.
-OPTIONAL_PARALLEL_DIRS := clang
+
+ifneq ($(CLANG_SRC_ROOT),)
+  OPTIONAL_PARALLEL_DIRS := $(CLANG_SRC_ROOT)
+else
+  OPTIONAL_PARALLEL_DIRS := clang
+endif
 
 # Build LLDB if present. Note LLDB must be built last as it depends on the
 # wider LLVM infrastructure (including Clang).
@@ -36,9 +43,6 @@ ifdef ONLY_TOOLS
   PARALLEL_DIRS := $(filter-out lldb,$(ONLY_TOOLS))
 endif
 
-include $(LEVEL)/Makefile.config
-
-
 # These libraries build as dynamic libraries (.dylib /.so), they can only be
 # built if ENABLE_PIC is set.
 ifndef ONLY_TOOLS