Slim down static binaries by avoiding stdio.

It's okay for a program to choose to drag in stdio, but it's unfortunate
if even the minimal "int main() { return 42; }" drags in stdio...

This brings the minimal static binary on ARM down from 78KiB to 46KiB.

Given that we don't have a separate -lpthread it's not obvious to me that
we can shave this down any further. I'm not sure whether this is a worthwhile
change for that reason. (And the fact that dynamic binaries, the usual case,
are unaffected either way.)

Change-Id: I02f91dcff37d14354314a30b72fed2563f431c88
diff --git a/libc/stdlib/atexit.c b/libc/stdlib/atexit.c
index 05f2faa..e10238b 100644
--- a/libc/stdlib/atexit.c
+++ b/libc/stdlib/atexit.c
@@ -103,7 +103,7 @@
 {
 	struct atexit *p = __atexit;
 	struct atexit_fn *fnp;
-	size_t pgsize = sysconf(_SC_PAGESIZE);
+	size_t pgsize = getpagesize();
 	int ret = -1;
 
 	if (pgsize < sizeof(*p))
@@ -219,7 +219,7 @@
 __atexit_register_cleanup(void (*func)(void))
 {
         struct atexit *p;
-        size_t pgsize = sysconf(_SC_PAGESIZE);
+        size_t pgsize = getpagesize();
 
         if (pgsize < sizeof(*p))
                 return;
@@ -248,4 +248,3 @@
 unlock:
         _ATEXIT_UNLOCK();
 }
-