Read Soong-exported configuration

This is to ensure that Make and Soong agree on configuration variables
like TARGET_GLOBAL_CFLAGS. Only a few variables are actually checked
currently until we make more actually the same.

Bug: 23566674
Change-Id: Ibede43d933ede4d470e182f9490ea6ec4ef52fbc
diff --git a/core/main.mk b/core/main.mk
index c455320..6401efc 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -107,6 +107,8 @@
 include build/core/ninja.mk
 else # KATI
 
+include $(SOONG_MAKEVARS_MK)
+
 # Write the build number to a file so it can be read back in
 # without changing the command line every time.  Avoids rebuilds
 # when using ninja.