Add RBE support for Javac, R8, and D8 if respective env vars are set.

Test: aosp_crosshatch build with and without the new variables.
Change-Id: I252ff5dd8e372edf8c86e25348c8a2bfab41d70d
diff --git a/core/soong_config.mk b/core/soong_config.mk
index d223792..95ff5ef 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -156,6 +156,9 @@
 
 $(call add_json_bool, UseGoma,                           $(filter-out false,$(USE_GOMA)))
 $(call add_json_bool, UseRBE,                            $(filter-out false,$(USE_RBE)))
+$(call add_json_bool, UseRBEJAVAC,                       $(filter-out false,$(RBE_JAVAC)))
+$(call add_json_bool, UseRBER8,                          $(filter-out false,$(RBE_R8)))
+$(call add_json_bool, UseRBED8,                          $(filter-out false,$(RBE_D8)))
 $(call add_json_bool, Arc,                               $(filter true,$(TARGET_ARC)))
 
 $(call add_json_list, NamespacesToExport,                $(PRODUCT_SOONG_NAMESPACES))