kbuild: Fix extracting of CONFIG_ references

by Sam Ravnborg:

fixdep, when adding dependencies to config entires fails to take into account
the last part of a config entry, if it contains more than one underscore.
Example:
CONFIG_PROC_FS generates
$(wildcard include/config/proc.h)
but should generate
$(wildcard include/config/proc/fs.h)

Attached patch fixes this.

scripts/fixdep.c

@@ -238,7 +238,7 @@ void parse_config_file(char *map, size_t len)
 		if (memcmp(p, "CONFIG_", 7))
 			continue;
 		for (q = p + 7; q < map + len; q++) {
-			if (!(isalnum(*q)))
+			if (!(isalnum(*q) || *q == '_'))
 				goto found;
 		}
 		continue;