Allow projects to define their own globally-available variables

Bug: 73178261
Test: make checkbuild
Change-Id: I53ee0f1d3ec072e19f4893cca44e16ef672fabfe
diff --git a/core/config.mk b/core/config.mk
index b28bb58..d89e2f8 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -115,6 +115,9 @@
 # Various mappings to avoid hard-coding paths all over the place
 include $(BUILD_SYSTEM)/pathmap.mk
 
+# Allow projects to define their own globally-available variables
+include $(BUILD_SYSTEM)/project_definitions.mk
+
 # ###############################################################
 # Build system internal files
 # ###############################################################