Export DIST_DIR to soong on dist builds.

Bug: 64267858

Test: Adding DistDir to build/soong/android/variable.go enables access
      to DIST_DIR_SOONG.

Change-Id: I74faea11255edf37db6a4eaf193df300c363bfb7
diff --git a/core/config.mk b/core/config.mk
index bebc186..3f503ad 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -67,6 +67,9 @@
 
 ORIGINAL_MAKECMDGOALS := $(MAKECMDGOALS)
 
+dist_goal := $(strip $(filter dist,$(MAKECMDGOALS)))
+MAKECMDGOALS := $(strip $(filter-out dist,$(MAKECMDGOALS)))
+
 # Tell python not to spam the source tree with .pyc files.  This
 # only has an effect on python 2.6 and above.
 export PYTHONDONTWRITEBYTECODE := 1
diff --git a/core/distdir.mk b/core/distdir.mk
index 89c5966..c074186 100644
--- a/core/distdir.mk
+++ b/core/distdir.mk
@@ -17,9 +17,6 @@
 # When specifying "dist", the user has asked that we copy the important
 # files from this build into DIST_DIR.
 
-dist_goal := $(strip $(filter dist,$(MAKECMDGOALS)))
-MAKECMDGOALS := $(strip $(filter-out dist,$(MAKECMDGOALS)))
-
 ifdef dist_goal
 
 # $(1): source file
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 5ebd123..a90e5af 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -119,6 +119,8 @@
 
 $(call add_json_bool, UseGoma,                           $(filter-out false,$(USE_GOMA)))
 
+$(call add_json_str,  DistDir,                           $(if $(dist_goal), $(DIST_DIR)))
+
 _contents := $(subst $(comma)$(newline)__SV_END,$(newline)}$(newline),$(_contents)__SV_END)
 
 $(file >$(SOONG_VARIABLES).tmp,$(_contents))