remove external linkage from __simple_malloc definition

this function is used only as a weak definition for malloc, for static
linking in programs which do not call realloc or free. since it had
external linkage and was thereby exported in libc.so's dynamic symbol
table, --gc-sections was unable to drop it. this was merely an
oversight; there's no reason for it to be external, so make it static.

src/malloc/lite_malloc.c

@@ -8,7 +8,7 @@
 
 void *__expand_heap(size_t *);
 
-void *__simple_malloc(size_t n)
+static void *__simple_malloc(size_t n)
 {
 	static char *cur, *end;
 	static volatile int lock[2];