Include stdint.h in zstd_jni for uintptr_t

macOS clang pulls stdint.h in transitively via stdlib.h, so the build
was passing on darwin but failing on the manylinux2014 GCC that the
linux-x86-64 and linux-aarch64 workflow jobs use. Add the explicit
include so every supported toolchain compiles cleanly.

Author: bluestreak01

core/src/main/c/share/zstd_jni.c

@@ -34,6 +34,7 @@
  */
 
 #include <jni.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include "zstd.h"