Disable unsigned-shift-base by default.

New clang compiler enables unsigned-shift-base as part of
integer sanitizers. But it makes some daemons crash at
libc++.

Bug: 177566116
Test: build.
Change-Id: I6d64fa5002b6035be4d960441eb5176c97152af9

core/config_sanitizers.mk

@@ -441,3 +441,13 @@ ifneq ($(findstring fsanitize,$(my_cflags)),)
     endif
   endif
 endif
+
+# http://b/177566116, libc++ may crash with this sanitizer.
+# Disable this check unless it has been explicitly specified.
+ifneq ($(findstring fsanitize,$(my_cflags)),)
+  ifneq ($(findstring integer,$(my_cflags)),)
+    ifeq ($(findstring sanitize=unsigned-shift-base,$(my_cflags)),)
+      my_cflags += -fno-sanitize=unsigned-shift-base
+    endif
+  endif
+endif