No .
is not allowed in macro names since they are identifiers and identifiers are not allowed to include a .
. We can see this by going to draft C99 standard section 6.10
Preprocessing directives which includes the following grammar:
# define identifier replacement-list new-line
# define identifier lparen identifier-listopt ) replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... ) replacement-list new-line
^^^^^^^^^^
and section 6.4.2
Identifiers covers what is a valid identifier.