build system: stop including alloca.h, stdlib.h provides it

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/scripts/basic/docproc.c b/scripts/basic/docproc.c
index b125698..7f21443 100644
--- a/scripts/basic/docproc.c
+++ b/scripts/basic/docproc.c
@@ -39,7 +39,7 @@
 #include <limits.h>
 #include <sys/types.h>
 #include <sys/wait.h>
-#include <alloca.h>
+//bbox disabled: #include <alloca.h>
 
 /* exitstatus is used to keep track of any failing calls to kernel-doc,
  * but execution continues. */