Put libcore generated source files into LOCAL_INTERMEDIATES_SOURCES

LOCAL_SRC_FILES is expected to be a list of files relative to the
Android.mk files.  If OUT_DIR is absolute then adding generated
files to the list produces bad paths when $(LOCAL_PATH)/ is prepended
to it.  Put libcore's generated sources into
LOCAL_INTERMEDIATE_SOURCES instead.

Bug: 64930165
Bug: 68375156
Test: m checkbuild
Change-Id: I4b36fd192570ea0cd52d8537a16c078c726d97fd