Adding a TODO for ELF x86-32 support on MSVC.

iree/hal/local/elf/arch/x86_32.c

diff --git a/iree/hal/local/elf/arch/x86_32.c b/iree/hal/local/elf/arch/x86_32.c
index 6a7c103..05d08d7 100644
--- a/iree/hal/local/elf/arch/x86_32.c
+++ b/iree/hal/local/elf/arch/x86_32.c
@@ -120,10 +120,10 @@
 // Cross-ABI function calls
 //==============================================================================
 
-// System V 386 ABI (used in IREE):
+// System V i386 ABI (used in IREE):
 // https://uclibc.org/docs/psABI-i386.pdf
 // Arguments:
-//
+//   (reverse order on the stack; last arg furthest from stack pointer)
 //
 // Results:
 //   EAX
@@ -136,7 +136,7 @@
 
 #if defined(IREE_PLATFORM_WINDOWS)
 
-#error "TODO"
+#error "TODO(#6554): need cdecl -> sysv ABI shims in x86_32_msvc.asm"
 
 #else