Enable SKIP_BOOT_JARS_CHECK by default when instrumenting

Bug: 36792868
Test: make -j EMMA_INSTRUMENT=true
Change-Id: I8f52418c97adc67c4c0a02ef8e2b84be620a6aee
diff --git a/core/main.mk b/core/main.mk
index d14d64b..97eb5a5 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -93,11 +93,21 @@
 # (must be defined before including definitions.make)
 INTERNAL_MODIFIER_TARGETS := all
 
-# EMMA_INSTRUMENT_STATIC merges the static emma library to each emma-enabled module.
+# EMMA_INSTRUMENT_STATIC merges the static jacoco library to each
+# jacoco-enabled module.
 ifeq (true,$(EMMA_INSTRUMENT_STATIC))
 EMMA_INSTRUMENT := true
 endif
 
+ifeq (true,$(EMMA_INSTRUMENT))
+# Adding the jacoco library can cause the inclusion of
+# some typically banned classes
+# So if the user didn't specify SKIP_BOOT_JARS_CHECK, enable it here
+ifndef SKIP_BOOT_JARS_CHECK
+SKIP_BOOT_JARS_CHECK := true
+endif
+endif
+
 #
 # -----------------------------------------------------------------
 # Validate ADDITIONAL_DEFAULT_PROPERTIES.