Update a comment to be more intention-revealing.

And also inclusive of riscv64.

Test: treehugger
Change-Id: I27280e1d934ce3bb47026820b75850c824801022
diff --git a/tests/signal_test.cpp b/tests/signal_test.cpp
index 7f7f3db..fa648d2 100644
--- a/tests/signal_test.cpp
+++ b/tests/signal_test.cpp
@@ -823,9 +823,9 @@
 #endif
 
 TEST(signal, sigset_size) {
-  // The setjmp implementations assume that sigset_t can fit in a
-  // long. This is true because ARM and x86 have broken rt signal support,
-  // and AArch64 and x86_64 both have a SIGRTMAX defined as 64.
+  // The setjmp implementations assume that sigset_t can fit in a long.
+  // This is true because the 32-bit ABIs have broken rt signal support,
+  // but the 64-bit ABIs both have a SIGRTMAX defined as 64.
 #if defined(__BIONIC__)
   static_assert(sizeof(sigset_t) <= sizeof(long), "sigset_t doesn't fit in a long");
 #endif