headers/wintrust: Add forward declarations for structs

Like in 0028c5c24f84750b5a53131c69e5f69fb51d8a7c, this solves warnings like

   mingw-w64-headers/include/wintrust.h:245:47: warning: 'struct _CRYPT_PROVIDER_DATA' declared inside parameter list will not be visible outside of this definition or declaration
     245 |   typedef WINBOOL (*PFN_CPD_ADD_STORE)(struct _CRYPT_PROVIDER_DATA *pProvData,HCERTSTORE hStore2Add);
         |                                               ^~~~~~~~~~~~~~~~~~~~
   mingw-w64-headers/include/wintrust.h:246:124: warning: 'struct _CRYPT_PROVIDER_SGNR' declared inside parameter list will not be visible outside of this definition or declaration
     246 |   typedef WINBOOL (*PFN_CPD_ADD_SGNR)(struct _CRYPT_PROVIDER_DATA *pProvData,WINBOOL fCounterSigner,DWORD idxSigner,struct _CRYPT_PROVIDER_SGNR *pSgnr2Add);
         |                                                                                                                            ^~~~~~~~~~~~~~~~~~~~

Without these forward declarations the typedefs declare new local types that
are not the same types as those in file scope.

Signed-off-by: LIU Hao <lh_mouse@126.com>
diff --git a/mingw-w64-headers/include/wintrust.h b/mingw-w64-headers/include/wintrust.h
index 22e03f2..68221d0 100644
--- a/mingw-w64-headers/include/wintrust.h
+++ b/mingw-w64-headers/include/wintrust.h
@@ -240,6 +240,11 @@
 
 #define TRUSTERROR_MAX_STEPS 38
 
+  struct _CRYPT_PROVIDER_DATA;
+  struct _CRYPT_PROVIDER_SGNR;
+  struct _CRYPT_PROVIDER_PRIVDATA;
+  struct _CRYPT_PROVIDER_DEFUSAGE;
+
   typedef void *(*PFN_CPD_MEM_ALLOC)(DWORD cbSize);
   typedef void (*PFN_CPD_MEM_FREE)(void *pvMem2Free);
   typedef WINBOOL (*PFN_CPD_ADD_STORE)(struct _CRYPT_PROVIDER_DATA *pProvData,HCERTSTORE hStore2Add);