C: Fix missing spaces in 'struct' fix-it hints

C: Fix missing spaces in 'struct' fix-it hints

In r237714 I added fix-it hints to the C frontend for missing "struct"
keywords e.g.:

spellcheck-typenames.c:69:1: error: unknown type name ‘foo_t’; use
‘struct’ keyword to refer to the type
 foo_t *foo_ptr;
 ^~~~~
 struct

However when using the (not yet in trunk) option
 -fdiagnostics-generate-patch,
the generated patch is nonsensical:

  -foo_t *foo_ptr;
  +structfoo_t *foo_ptr;

Fix the fix-its by adding a trailing space to each one, giving:

  -foo_t *foo_ptr;
  +struct foo_t *foo_ptr;

gcc/c/ChangeLog:
	* c-parser.c (c_parser_declaration_or_fndef): Add trailing space
	to the insertion fixits for "struct", "union", and "enum".

From-SVN: r239912