reenable the use of sbrk on wasm as it seems more stable than direct memory_grow

src/os.c

@@ -8,6 +8,8 @@ terms of the MIT license. A copy of the license can be found in the file
 #define _DEFAULT_SOURCE   // ensure mmap flags are defined
 #endif
 
+#define MI_USE_SBRK
+
 #if defined(__sun)
 // illumos provides new mman.h api when any of these are defined
 // otherwise the old api based on caddr_t which predates the void pointers one.
@@ -26,6 +28,10 @@ terms of the MIT license. A copy of the license can be found in the file
 #pragma warning(disable:4996)  // strerror
 #endif
 
+#if defined(__wasi__)
+#define MI_USE_SBRK
+#endif
+
 #if defined(_WIN32)
 #include <windows.h>
 #elif defined(__wasi__)