env: Use static_assert() to check if default_environment is too large

Check sizeof(default_environment) against ENV_SIZE in a static_assert()
instead of runtime.
Only check if !USE_HOSTCC (for in fw_env tool ENV_SIZE expands to a
variable, and cannot be checked statically) nad
!DEFAULT_ENV_INSTANCE_EMBEDDED, for in that case the default_environment
variable is not set.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/env_default.h

@@ -121,3 +121,9 @@ const char default_environment[] = {
 	}
 #endif
 };
+
+#if !defined(USE_HOSTCC) && !defined(DEFAULT_ENV_INSTANCE_EMBEDDED)
+#include <env_internal.h>
+static_assert(sizeof(default_environment) <= ENV_SIZE,
+	      "Default environment is too large");
+#endif