I was successful compiling sbcl latest on mingw64.  Below are some notes differences that I noted between the compilation log on mingw64 (attached here for you to review) and the compilation log on mwing32.  I don't know if they are relevant to the problem but I'll mention them anyway.

- mingw64 compiles -g -O5, mingw32 compiled with -g -O3
- mingw32 compiles with -D_WIN32_WINNT=0x600 vs mingw64 compiles with -DWINVER=0x0501.  Intuitively it feels it should be the opposite?
- mingw32 compiles with -mpreferred-stack-boundary=2, this option is not in mingw64.  What is the purpose of this option?
- mingw64 compiles with  -Wno-unused-function -Wno-unused-parameter -Wno-cast-function-type 
- Compiling cross-float.fasl-tmp in win32 generated the following message (there were other occurrences that didn't occur in mingw64)
//CROSS-FLOAT DISCREPANCY!
// CACHE: (COMMON-LISP:EXPT #.(MAKE-DOUBLE-FLOAT #x40240000 #x0) -309) -> (#.(MAKE-DOUBLE-FLOAT #xB815 #x7268FDAF))
// HOST : (9.999928873692877d-310)
- mingw32 warns the following
in gc-common.c,
gc-common.c:1851:16: warning: 'can_invoke_post_gc' defined but not used [-Wunused-function]
 1851 | static boolean can_invoke_post_gc(__attribute__((unused)) struct thread* th,
in  interrupt.c, 
interrupt.c:1260:1: warning: 'run_deferred_handler' defined but not used [-Wunused-function]
 1260 | run_deferred_handler(struct interrupt_data *data, os_context_t *context)
      | ^~~~~~~~~~~~~~~~~~~~
interrupt.c:710:1: warning: 'check_interrupt_context_or_lose' defined but not used [-Wunused-function]
  710 | check_interrupt_context_or_lose(os_context_t *context)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
interrupt.c:167:13: warning: 'sigmask_logior' defined but not used [-Wunused-function]
  167 | static void sigmask_logior(sigset_t *dest, const sigset_t *source)
      |             ^~~~~~~~~~~~~~
in monitor.c:507
monitor.c:507:1: warning: 'sigint_handler' defined but not used [-Wunused-function]
  507 | sigint_handler(int __attribute__((unused)) signal,
      | ^~~~~~~~~~~~~~
in win32-os.c 
At top level:
win32-os.c:729:15: warning: 'qpcMultiplier' defined but not used [-Wunused-variable]
  729 | static double qpcMultiplier;
      |               ^~~~~~~~~~~~~
win32-os.c:728:22: warning: 'lisp_init_time' defined but not used [-Wunused-variable]
  728 | static LARGE_INTEGER lisp_init_time;
      |                      ^~~~~~~~~~~~~~

- in fd-stream.lisp
; file: D:/Downloads/sbcl_latest/sbcl/src/code/fd-stream.lisp
; in: DEFUN SB-IMPL::!MAKE-COLD-STDERR-STREAM
;     (SB-WIN32::GET-STD-HANDLE-OR-NULL SB-WIN32::+STD-ERROR-HANDLE+)
; 
; caught WARNING:
;   undefined variable: SB-WIN32::+STD-ERROR-HANDLE+
; 
; compilation unit finished
;   Undefined variable:
;     SB-WIN32::+STD-ERROR-HANDLE+
;   caught 1 WARNING condition
;   printed 12 notes

Likely suspicious calls:
   1 SB-EXT:GET-TIME-OF-DAY

Possibly suspicious calls:
 194 SB-KERNEL:%COERCE-CALLABLE-TO-FUN
 181 SB-KERNEL:SPECIFIER-TYPE
 162 SB-KERNEL:%DOUBLE-FLOAT
  94 SB-KERNEL:%SINGLE-FLOAT
  33 SB-KERNEL:%UNARY-TRUNCATE/DOUBLE-FLOAT
  24 (SETF SB-INT:INFO)
  15 SB-KERNEL:%UNARY-TRUNCATE/SINGLE-FLOAT
   9 SB-INT:INFO
   8 SB-KERNEL:VALUES-SPECIFIER-TYPE
   5 SB-C::MASK-SIGNED-FIELD
   5 SB-KERNEL:%UNARY-ROUND
   1 SB-VM::ASH-LEFT-MODFX
   1 SB-SYS:FOREIGN-SYMBOL-SAP
   1 SB-KERNEL:DSD-INDEX

- mingw64 in safepoint.c, complains about fall through cases that mingw32 doesn't complain
safepoint.c: In function 'gc_stop_the_world':
safepoint.c:853:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
  853 |             gc_advance(GC_QUIET,gc_state.phase);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
safepoint.c:854:9: note: here
  854 |         case GC_FLIGHT:
      |         ^~~~
safepoint.c:857:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
  857 |             if ((gc_state.phase == GC_MESSAGE)
      |                ^
safepoint.c:868:9: note: here
  868 |         case GC_QUIET:
      |         ^~~~


Let me know if there is anything I can do to help.