Some of my testing exposed a minor problem in GCC 9's validation
of the type of function parameters referred to by attribute
positional arguments.  Whereas GCC 8 accepts all C integer types,
including enumerated types, such as:

   enum AllocAlign { Align16 = 16, Align32 = 32 };

   __attribute__ ((alloc_align (1))) void*
   alloc (size_t, enum AllocAlign)

GCC 9 only accepts signed and unsigned integer types.  This change
(introduced by myself) was unintentional, and a fix for it is in
the attached trivial patch.  I plan to commit it without approval
in the next day or so unless any concerns or suggestions come up.

Tested on x86_64-linux.

Martin