Fix installheaders target to do what it did prior to r161760. rdar://12348765

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@164413 91177308-0d34-0410-b5e6-96231b3b80d8

Makefile

@@ -30,7 +30,16 @@ installsrc:: $(SRCROOT)
 
 clean::
 
+# The installheaders target is used by clang's runtime/libcxx makefile.
 installheaders::
+	mkdir -p $(HEADER_DIR)/c++/v1/ext
+	rsync -r --exclude=".*" --exclude="support" $(SRCDIRS)/include/* \
+	  $(HEADER_DIR)/c++/v1/
+	chown -R root:wheel $(HEADER_DIR)/c++
+	chmod 755 $(HEADER_DIR)/c++/v1
+	chmod 644 $(HEADER_DIR)/c++/v1/*
+	chmod 755 $(HEADER_DIR)/c++/v1/ext
+	chmod 644 $(HEADER_DIR)/c++/v1/ext/*
 
 install::