dtc: cpp co-existence: add support for #line directives

Line control directives of the following formats are supported:
    #line LINE "FILE"
    # LINE "FILE" [FLAGS]

This allows dtc to consume the output of pre-processors, and to provide
error messages that refer to the original filename, including taking
into account any #include directives that the pre-processor may have
performed.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>

srcpos.h

@@ -113,4 +113,6 @@ extern void srcpos_error(struct srcpos *pos, char const *, ...)
 extern void srcpos_warn(struct srcpos *pos, char const *, ...)
      __attribute__((format(printf, 2, 3)));
 
+extern void srcpos_set_line(char *f, int l);
+
 #endif /* _SRCPOS_H_ */