KernelUtils.h - better static assert messages for impossible conditions

per Lorenzo's request during cherrypick to udc-dev on
https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/libs/net/+/23391171

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ib19f5b3b63a6978ac5a72b2be08a2f0ba6cdd712
diff --git a/staticlibs/native/bpf_headers/include/bpf/KernelUtils.h b/staticlibs/native/bpf_headers/include/bpf/KernelUtils.h
index 769ec4b..59257b8 100644
--- a/staticlibs/native/bpf_headers/include/bpf/KernelUtils.h
+++ b/staticlibs/native/bpf_headers/include/bpf/KernelUtils.h
@@ -57,11 +57,11 @@
 }
 
 #if defined(__LP64__)
-static_assert(isUserspace64bit(), "huh?");
+static_assert(isUserspace64bit(), "huh? LP64 must have 64-bit userspace");
 #elif defined(__ILP32__)
-static_assert(isUserspace32bit(), "huh?");
+static_assert(isUserspace32bit(), "huh? ILP32 must have 32-bit userspace");
 #else
-#error "huh?"
+#error "huh? must be either LP64 (64-bit userspace) or ILP32 (32-bit userspace)"
 #endif
 
 static_assert(isUserspace32bit() || isUserspace64bit(), "must be either 32 or 64 bit");