Use hermetic ckati/makeparallel prebuilts

Currently, we're building against the native host version of libc++ and
other headers. Instead, use prebuilts of ckati/makeparallel built with
Soong against the included libc++ and sysroot. Building ckati /
makeparallel doesn't work well in unbundled branches that don't have all
of the libc++ dependencies to do successful host builds.

KATI is default variable defined when running under Kati, don't use it
for other purposes. Use CKATI instead.

Bug: 27533820
Change-Id: I82d66f5e34e3341a3cee4c5c83cd1d9a54d057ff
diff --git a/core/soong.mk b/core/soong.mk
index f48e15e..176c159 100644
--- a/core/soong.mk
+++ b/core/soong.mk
@@ -4,9 +4,6 @@
 SOONG_ANDROID_MK := $(SOONG_OUT_DIR)/Android.mk
 SOONG_VARIABLES := $(SOONG_OUT_DIR)/soong.variables
 SOONG_IN_MAKE := $(SOONG_OUT_DIR)/.soong.in_make
-SOONG_HOST_EXECUTABLES := $(SOONG_OUT_DIR)/host/$(HOST_PREBUILT_TAG)/bin
-KATI := $(SOONG_HOST_EXECUTABLES)/ckati
-MAKEPARALLEL := $(SOONG_HOST_EXECUTABLES)/makeparallel
 
 ifeq (,$(filter /%,$(SOONG_OUT_DIR)))
 SOONG_TOP_RELPATH := $(shell python -c "import os; print os.path.relpath('$(TOP)', '$(SOONG_OUT_DIR)')")
@@ -63,7 +60,4 @@
 
 # Build an Android.mk listing all soong outputs as prebuilts
 $(SOONG_ANDROID_MK): $(SOONG) $(SOONG_VARIABLES) $(SOONG_IN_MAKE) FORCE
-	$(hide) $(SOONG) $(KATI) $(MAKEPARALLEL) $(NINJA_ARGS)
-
-$(KATI): $(SOONG_ANDROID_MK)
-$(MAKEPARALLEL): $(SOONG_ANDROID_MK)
+	$(hide) $(SOONG) $(SOONG_BUILD_NINJA) $(NINJA_ARGS)