aic7xxx: Fix re-building firmware with -fno-common

The generated C output for aicasm_scan.l defines yylineno already, so
references to it from other files should use an extern declaration.

The STAILQ_HEAD use in aicasm_symbol.h also provided an identifier,
causing it to both define the struct type and define a variable of that
struct type, causing any C file including the header to define the same
variable. This variable is not used (and confusingly clashes with a
field name just below) and was likely caused by confusion when switching
between defining fields using similar type macros and defining the type
itself.

Reviewed by:	imp
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D30525

sys/dev/aic7xxx/aicasm/aicasm_gram.y

@@ -59,7 +59,7 @@
 #include "aicasm_symbol.h"
 #include "aicasm_insformat.h"
 
-int yylineno;
+extern int yylineno;
 char *yyfilename;
 char stock_prefix[] = "aic_";
 char *prefix = stock_prefix;

sys/dev/aic7xxx/aicasm/aicasm_symbol.h

@@ -110,7 +110,7 @@ struct macro_arg {
 	regex_t	arg_regex;
 	char   *replacement_text;
 };
-STAILQ_HEAD(macro_arg_list, macro_arg) args;
+STAILQ_HEAD(macro_arg_list, macro_arg);
 
 struct macro_info {
 	struct macro_arg_list args;