config/msvc.h: fill in gaps versus configure.ac/config.h.in

Cross-referenced configure.ac's AC_CHECK_HEADERS/AC_CHECK_FUNCS/PA_*
tests (as materialized into config/config.h.in) against config/msvc.h
and added definitions for macros MSVC actually supports:

- HAVE_STDARG_H, HAVE_STDIO_H, HAVE_WCHAR_H: always present.
- HAVE_STDINT_H: available starting with Visual Studio 2010
  (_MSC_VER >= 1600).
- HAVE_INTRIN_H plus an #include <intrin.h>, gated on Visual Studio
  2005 (_MSC_VER >= 1400) when the header was introduced.
- HAVE_ISCNTRL: always present.
- HAVE_ISASCII plus '#define isascii __isascii', since MSVC only
  provides the underscore-prefixed spelling.
- HAVE__BYTESWAP_USHORT/_ULONG/_UINT64: always present, declared in
  <stdlib.h>, matching the names PA_FIND_FUNC probes for in
  autoconf/m4/pa_endian.m4.
- HAVE__BITSCANREVERSE (>=1400) and HAVE__BITSCANREVERSE64 (>=1400 and
  only on _M_X64/_M_ARM64, since the 64-bit intrinsic does not exist
  on 32-bit x86).
- HAVE_UNSIGNED_LONG_LONG_INT: always present.
- HAVE_UINTMAX_T, gated on '#ifdef HAVE_STDINT_H' rather than a
  separate version check, with a textual 'unsigned long long'
  fallback for uintmax_t otherwise; gating strictly on HAVE_STDINT_H
  avoids the fallback macro clobbering <stdint.h>'s own uintmax_t
  typedef when both would otherwise be available.

Deliberately left out anything that is POSIX/GNU/BSD-only or does not
exist verbatim on MSVC (strcasecmp/strsep/strlcpy/mempcpy, getuid/
getrlimit/realpath, GCC __builtin_*/attribute probes, byteswap.h/
endian.h family, C23 stdbit.h, etc.), since compiler.h and the
relevant call sites already handle those cases separately for MSVC.

Verified with x86_64-w64-mingw32-gcc -fsyntax-only using manually
defined _MSC_VER/_M_X64/_M_ARM64 across Visual Studio versions
1310/1400/1600/1800/1929 (mingw-w64 declares the same intrinsics in
the expected headers), then confirmed end-to-end with a real MSVC
(cl.exe/nmake) build in CI.

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

config/msvc.h

@@ -25,6 +25,12 @@
 #ifndef NASM_CONFIG_MSVC_H
 #define NASM_CONFIG_MSVC_H
 
+/* Needed for the _BitScanReverse()/_BitScanReverse64() intrinsics below;
+   not available prior to Visual Studio 2005. */
+#if _MSC_VER >= 1400
+# include <intrin.h>
+#endif
+
 /* Define to 1 if you have the <fcntl.h> header file. */
 #define HAVE_FCNTL_H 1
 
@@ -33,9 +39,25 @@
 # define HAVE_INTTYPES_H 1
 #endif
 
+/* Define to 1 if you have the <intrin.h> header file. */
+#if _MSC_VER >= 1400
+# define HAVE_INTRIN_H 1
+#endif
+
 /* Define to 1 if you have the <io.h> header file. */
 #define HAVE_IO_H 1
 
+/* Define to 1 if you have the <stdarg.h> header file. */
+#define HAVE_STDARG_H 1
+
+/* Define to 1 if you have the <stdint.h> header file. */
+#if _MSC_VER >= 1600
+# define HAVE_STDINT_H 1
+#endif
+
+/* Define to 1 if you have the <stdio.h> header file. */
+#define HAVE_STDIO_H 1
+
 /* Define to 1 if you have the <stdlib.h> header file. */
 #define HAVE_STDLIB_H 1
 
@@ -48,6 +70,9 @@
 /* Define to 1 if you have the <sys/types.h> header file. */
 #define HAVE_SYS_TYPES_H 1
 
+/* Define to 1 if you have the <wchar.h> header file. */
+#define HAVE_WCHAR_H 1
+
 /* Define to 1 if you have the `access' function. */
 #define HAVE_ACCESS 1
 #if _MSC_VER < 1400
@@ -60,6 +85,13 @@
 # define fileno _fileno
 #endif
 
+/* Define to 1 if you have the `isascii' function. */
+#define HAVE_ISASCII 1
+#define isascii __isascii
+
+/* Define to 1 if you have the `iscntrl' function. */
+#define HAVE_ISCNTRL 1
+
 /* Define to 1 if you have the `snprintf' function. */
 #define HAVE_SNPRINTF 1
 #if _MSC_VER < 1900
@@ -77,6 +109,25 @@
 /* Define to 1 if you have the `_filelengthi64' function. */
 #define HAVE__FILELENGTHI64 1
 
+/* Define to 1 if you have the `_byteswap_ushort' intrinsic function. */
+#define HAVE__BYTESWAP_USHORT 1
+
+/* Define to 1 if you have the `_byteswap_ulong' intrinsic function. */
+#define HAVE__BYTESWAP_ULONG 1
+
+/* Define to 1 if you have the `_byteswap_uint64' intrinsic function. */
+#define HAVE__BYTESWAP_UINT64 1
+
+/* Define to 1 if you have the `_BitScanReverse' intrinsic function. */
+#if _MSC_VER >= 1400
+# define HAVE__BITSCANREVERSE 1
+#endif
+
+/* Define to 1 if you have the `_BitScanReverse64' intrinsic function. */
+#if (defined(_M_X64) || defined(_M_ARM64)) && _MSC_VER >= 1400
+# define HAVE__BITSCANREVERSE64 1
+#endif
+
 /* Define to 1 if you have the `_fseeki64' function. */
 #define HAVE__FSEEKI64 1
 
@@ -132,6 +183,18 @@
 # define uintptr_t size_t
 #endif
 
+/* Define to 1 if the system has the type `uintmax_t'. */
+#ifdef HAVE_STDINT_H
+# define HAVE_UINTMAX_T 1
+#else
+/* Define to the widest unsigned integer type if <stdint.h> and <inttypes.h>
+   do not define. */
+# define uintmax_t unsigned long long
+#endif
+
+/* Define to 1 if the system has the type `unsigned long long int'. */
+#define HAVE_UNSIGNED_LONG_LONG_INT 1
+
 /* Define to 1 if you have the `vsnprintf' function. */
 #define HAVE_VSNPRINTF 1
 #if _MSC_VER < 1400