tests/qapi-schema: Rename a few conditionals

tests/qapi-schema: Rename a few conditionals

Positive test case

    { 'enum': 'TestIfEnum',
      'data': [ 'foo', { 'name' : 'bar', 'if': 'TEST_IF_ENUM_BAR' } ],
      'if': 'TEST_IF_ENUM' }

generates

    #if defined(TEST_IF_ENUM)
    typedef enum TestIfEnum {
	TEST_IF_ENUM_FOO,
    #if defined(TEST_IF_ENUM_BAR)
	TEST_IF_ENUM_BAR,
    #endif /* defined(TEST_IF_ENUM_BAR) */
	TEST_IF_ENUM__MAX,
    } TestIfEnum;

Macro TEST_IF_ENUM_BAR clashes with the enumeration constant.
Wouldn't compile with -DTEST_IF_BAR.

Rename the macro to TEST_IF_ENUM_MEMBER.  For consistency, rename
similar macros elsewhere as well.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230316071325.492471-11-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>