Adding support for the new HDRMACRO builtin.
The latter is used to specify a file containing macro
definitions that are later used in #include statements,
as in:
#include MYFILE_H
A line like:
HDRMACRO mydefs.h ;
will parse the file "mydefs.h" for lines of the form:
#define MACRO <.......> and
#define MACRO "......."
and will store their definition in a global dictionary.
When a line like
#include MACRO
is later found during header file processing, the macro
will be resolved accordingly..