Fix invalid test generation by utils/ABITest/ABITestGen.py when the same enum is generated more than once.

When generating records/unions, the same enum type may be generated more
than once (with different names). In these cases, the name of the enum
values are not sufficiently unique to prevent multiple declarations. E.g:
  typedef enum T3 { enum0val0 } T3;
  typedef T3 T2[3];
  typedef enum T4 { enum0val0 } T4;
  typedef union T1 { T2 field0; T4 field1; char field2; } T1;

Added a unique suffix to enum values so that multiple identical enum types do
not use the same enum value names.

One example of this bug is produced by:
  ABITestGen.py --no-unsigned --no-vector --no-complex --no-bool \
                --max-args 0 --max-record-depth 1 -o inputs/test.9921.a.c \
                -T inputs/test.9921.b.c -D inputs/test.9921.driver.c \
                --min=9921 --count=1