include_regular_expression
--------------------------

Set the regular expression used for dependency checking.

::

  include_regular_expression(regex_match [regex_complain])

Set the regular expressions used in dependency checking.  Only files
matching regex_match will be traced as dependencies.  Only files
matching regex_complain will generate warnings if they cannot be found
(standard header paths are not searched).  The defaults are:

::

  regex_match    = "^.*$" (match everything)
  regex_complain = "^$" (match empty string only)
