[ASan] Fix large allocator test case to cope with 64k pages

[foad]

Summary

My PowerPC64 Linux box has 64k pages. The test assumes 4k pages. Fix it.

[samsonov]

LGTM

test/asan/TestCases/Posix/large_allocator_unpoisons_on_free.cc

 // Test that LargeAllocator unpoisons memory before releasing it to the OS.
 // RUN: %clangxx_asan %s -o %t
 // The memory is released only when the deallocated chunk leaves the quarantine,
 // otherwise the mmap(p, ...) call overwrites the malloc header.
 // RUN: ASAN_OPTIONS=quarantine_size=1 %run %t
 
 #include <assert.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #ifdef __ANDROID__
 #include <malloc.h>
 void *my_memalign(size_t boundary, size_t size) {
   return memalign(boundary, size);
 }
 #else
 void *my_memalign(size_t boundary, size_t size) {
   void *p;
   posix_memalign(&p, boundary, size);
   return p;
 }
 #endif
 
 int main() {
-  const int kPageSize = 4096;
+  const long kPageSize = sysconf(_SC_PAGESIZE);
   void *p = my_memalign(kPageSize, 1024 * 1024);
   free(p);
 
   char *q = (char *)mmap(p, kPageSize, PROT_READ | PROT_WRITE,
                          MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
   assert(q == p);
 
   memset(q, 42, kPageSize);
 
   munmap(q, kPageSize);
   return 0;
 }