[test] Mark RISC-V pass-struct-by-value tests to avoid flaky status c…

…hanges.

Bug: #48645
Change-Id: I3729c7df81ad2089224bf886a8c5345cc857f026
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/324764
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>

tests/ffi/ffi.status

@@ -70,6 +70,9 @@ vmspecific_regress_37511_test: SkipByDesign # Symbols are not exposed on purpose
 vmspecific_regress_37780_test: SkipByDesign # Symbols are not exposed on purpose and are not linked in Windows Precompiled. dartbug.com/40579
 vmspecific_regress_51794_test: SkipByDesign # Symbols are not exposed on purpose and are not linked in Windows Precompiled. dartbug.com/40579
 
+[ $arch == riscv32 || $arch == riscv64 ]
+*structs_by_value*: Skip # https://dartbug.com/48645
+
 # These tests trigger and catch an abort (intentionally) and terminate the VM.
 # They're incompatible with ASAN because not all memory is freed when aborting and
 # with AppJit because the abort the VM before it can generate a snapshot.