Add LOCAL_NOSANITIZE.

This can be used to selectively disable individual sanitizers on a
target. For example, some parts of libc should be built with
SafeStack (when requested with SANITIZE_TARGET), but never with
AddressSanitizer. Current build rules specify LOCAL_SANITIZE := never
to disable AddressSanitizer; the idea is to change that to
LOCAL_NOSANITIZE := address thread.

Bug: 27729263
Change-Id: I2b770f2ce3faf6ad6798792327e96adb86fe4a4f

core/clear_vars.mk

@@ -189,6 +189,7 @@ LOCAL_DPI_VARIANTS:=
 LOCAL_DPI_FILE_STEM:=
 LOCAL_SANITIZE:=
 LOCAL_SANITIZE_RECOVER:=
+LOCAL_NOSANITIZE:=
 LOCAL_DBUS_PROXY_PREFIX:=
 LOCAL_INIT_RC:=
 LOCAL_MODULE_HOST_OS:=

core/config_sanitizers.mk

@@ -34,6 +34,11 @@ ifeq ($(LOCAL_SANITIZE),never)
   my_sanitize :=
 endif
 
+my_nosanitize = $(strip $(LOCAL_NOSANITIZE))
+ifneq ($(my_nosanitize),)
+  my_sanitize := $(filter-out $(my_nosanitize),$(my_sanitize))
+endif
+
 # TSAN is not supported on 32-bit architectures. For non-multilib cases, make
 # its use an error. For multilib cases, don't use it for the 32-bit case.
 ifneq ($(filter thread,$(my_sanitize)),)