abi tests: remove 'char' in the PRINT_CONSTANT macro

We explicitely handle signed and unsigned, and some compilers (MSVC)
do not like duplicate types.

Author: pbor

src/codegen/sys/tests.rs

@@ -276,7 +276,6 @@ fn generate_constant_c(
     _Generic((CONSTANT_NAME), \
         char *: "%s", \
         const char *: "%s", \
-        char: "%c", \
         signed char: "%hhd", \
         unsigned char: "%hhu", \
         short int: "%hd", \