compiler.h/file.c: include <windows.h> before Windows SDK headers

nasmlib/file.c included <stringapiset.h> directly (for
MultiByteToWideChar()/CompareStringOrdinal()) without first including
<windows.h>. Windows SDK headers like <stringapiset.h> are only
guaranteed to work when pulled in through the normal <windows.h>
pipeline, which sets up SDK-internal architecture macros (_X86_,
_AMD64_, ...) derived from the compiler's own _M_IX86/_M_X64/etc.
Including them directly skips that setup and can fail with a
'No Target Architecture' #error from <winnt.h> -- which is exactly
what happened building with a real cl.exe/nmake in CI.

Move the fix to include/compiler.h, since <windows.h> is needed
broadly for Windows-specific functionality and other source files may
hit the same problem in the future. Include it (with
WIN32_LEAN_AND_MEAN) right after the _MBCS define, guarded by _WIN32,
before anything else gets a chance to include a Windows SDK header on
its own. file.c's direct <stringapiset.h> include is now redundant and
removed; <wchar.h> is kept since it's still used for the wchar_t type.

Confirmed fixed with a real MSVC (cl.exe/nmake) build in CI.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: H. Peter Anvin (Intel)

include/compiler.h

@@ -24,6 +24,22 @@
 /* On Microsoft platforms we support multibyte character sets in filenames */
 #define _MBCS 1
 
+/*
+ * On Windows, a number of source files need Windows API declarations
+ * (e.g. MultiByteToWideChar(), CompareStringOrdinal()) that live in SDK
+ * headers such as <stringapiset.h>.  Those headers are only guaranteed
+ * to work when included via the normal <windows.h> pipeline, which sets
+ * up SDK-internal architecture macros (_X86_, _AMD64_, ...) that plain
+ * compiler-provided macros (_M_IX86, _M_X64, ...) do not satisfy on
+ * their own; including them directly can fail with "No Target
+ * Architecture" errors from <winnt.h>.  Pull in <windows.h> once, here,
+ * before anything else gets a chance to jump the queue.
+ */
+#ifdef _WIN32
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+#endif
+
 #include "autoconf/attribute.h"
 
 #ifdef HAVE_CONFIG_H

nasmlib/file.c

@@ -45,7 +45,8 @@
  */
 #ifdef _WIN32
 #include <wchar.h>
-#include <stringapiset.h>
+/* <windows.h> (which brings in MultiByteToWideChar()/CompareStringOrdinal()
+   via <stringapiset.h>) is already included by "compiler.h". */
 
 typedef wchar_t *os_filename;
 typedef wchar_t  os_fopenflag;