javac 9 -target 1.9: Move bootclasspath jars onto classpath.

When building with OpenJDK 9's javac with -source 1.9 -target 1.9,
a runtime image (with system modules) is used via the --system
command line flag, instead of --bootclasspath.
The runtime image only contains the default libraries (libcore)
but is missing other libraries that might be on the bootclasspath
for a particular build target.

This CL fixes compilation for this case by adding the missing
jars onto the classpath instead.

This already used to work but was broken by CL [1]. I attempted
to conditionally revert some of that CL's changes to java_common.mk
for the case of language level 1.9, but couldn't get it to work.
Therefore this CL follows a different approach.

[1] http://r.android.com/519552

Bug: 38177569
Test: Treehugger
Test: Ran "EXPERIMENTAL_USE_OPENJDK9=true make checkbuild docs"
      and spot-checked some javac invocations to confirm that the
      system modules libs were not included in the bootclasspath,
      but other libs were.

Change-Id: I48fd11aac9b310bfa58dee0f9cfb3ef33f10bca8

core/definitions.mk

@@ -2241,15 +2241,17 @@ $(hide) if [ -s $(PRIVATE_JAVA_SOURCE_LIST) ] ; then \
     $(SOONG_JAVAC_WRAPPER) $(JAVAC_WRAPPER) $(1) -encoding UTF-8 \
     $(if $(findstring true,$(PRIVATE_WARNINGS_ENABLE)),$(xlint_unchecked),) \
     $(if $(PRIVATE_USE_SYSTEM_MODULES), \
-      $(addprefix --system=,$(PRIVATE_SYSTEM_MODULES)), \
+      $(addprefix --system=,$(PRIVATE_SYSTEM_MODULES_DIR)), \
       $(addprefix -bootclasspath ,$(strip \
           $(call normalize-path-list,$(PRIVATE_BOOTCLASSPATH)) \
           $(PRIVATE_EMPTY_BOOTCLASSPATH)))) \
     $(if $(PRIVATE_USE_SYSTEM_MODULES), \
       $(if $(PRIVATE_PATCH_MODULE), \
         --patch-module=$(PRIVATE_PATCH_MODULE)=$(call normalize-path-list,. $(2)))) \
-    $(addprefix -classpath ,$(strip \
-        $(call normalize-path-list,$(2)))) \
+    $(addprefix -classpath ,$(call normalize-path-list,$(strip \
+      $(if $(PRIVATE_USE_SYSTEM_MODULES), \
+        $(filter-out $(PRIVATE_SYSTEM_MODULES_LIBS),$(PRIVATE_BOOTCLASSPATH))) \
+      $(2)))) \
     $(if $(findstring true,$(PRIVATE_WARNINGS_ENABLE)),$(xlint_unchecked),) \
     -d $(PRIVATE_CLASS_INTERMEDIATES_DIR) -s $(PRIVATE_ANNO_INTERMEDIATES_DIR) \
     $(PRIVATE_JAVACFLAGS) \

core/java_common.mk

@@ -358,7 +358,9 @@ endif
 
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_BOOTCLASSPATH := $(full_java_bootclasspath_libs)
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_EMPTY_BOOTCLASSPATH := $(empty_bootclasspath)
-$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_SYSTEM_MODULES := $(my_system_modules_dir)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_SYSTEM_MODULES := $(my_system_modules)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_SYSTEM_MODULES_DIR := $(my_system_modules_dir)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_SYSTEM_MODULES_LIBS := $(call java-lib-files,$(SOONG_SYSTEM_MODULES_LIBS_$(my_system_modules)))
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_PATCH_MODULE := $(LOCAL_PATCH_MODULE)
 
 ifndef LOCAL_IS_HOST_MODULE