these four warning options were overlooked previously, likely because
they're not part of GCC's -Wall. they all detect constraint violations
(invalid C at the source level) and should always be on in -Werror
form.
tryflag CFLAGS_AUTO -Werror=implicit-int
tryflag CFLAGS_AUTO -Werror=pointer-sign
tryflag CFLAGS_AUTO -Werror=pointer-arith
+tryflag CFLAGS_AUTO -Werror=int-conversion
+tryflag CFLAGS_AUTO -Werror=incompatible-pointer-types
+tryflag CFLAGS_AUTO -Werror=discarded-qualifiers
+tryflag CFLAGS_AUTO -Werror=discarded-array-qualifiers
#
# GCC ignores unused arguements by default, but Clang needs this extra