tools: env: include compiler.h

With gcc 5.2 and later we get a bunch of "error: unknown type name" for
'uint8_t', 'uint32_t' and friends.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>

tools/env/fw_env.c

@@ -10,6 +10,7 @@
 
 #define _GNU_SOURCE
 
+#include <compiler.h>
 #include <errno.h>
 #include <env_flags.h>
 #include <fcntl.h>