Unify preprocessor checks for win32

<https://sourceforge.net/p/predef/wiki/OperatingSystems/> says that _WIN32 is
always defined for both 32-bit and 64-bit versions of Windows.

c/bitvector-ops.c

@@ -3,9 +3,8 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <malloc.h>
-#define alloca _alloca
 #endif
 
 #include "dtypes.h"

c/bitvector.c

@@ -34,13 +34,13 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "dtypes.h"
-#include "bitvector.h"
-
-#ifdef WIN32
+#ifdef _WIN32
 #include <malloc.h>
 #endif
 
+#include "dtypes.h"
+#include "bitvector.h"
+
 uint32_t *bitvector_resize(uint32_t *b, uint64_t oldsz, uint64_t newsz,
                            int initzero)
 {

c/builtins.c

@@ -345,7 +345,7 @@ static value_t fl_path_cwd(value_t *args, uint32_t nargs)
     return FL_T;
 }
 
-#ifdef WIN32
+#ifdef _WIN32
 #define stat _stat
 #endif
 static value_t fl_path_exists(value_t *args, uint32_t nargs)

c/dtypes.h

@@ -13,24 +13,10 @@
   We assume the LP64 convention for 64-bit platforms.
 */
 
-#if defined(__gnu_linux__)
-#define LINUX
-#elif defined(__APPLE__) && defined(__MACH__)
-#define MACOSX
-#elif defined(__OpenBSD__)
-#define OPENBSD
-#elif defined(__FreeBSD__)
-#define FREEBSD
-#elif defined(_WIN32)
-#define WIN32
-#else
-#error "unknown platform"
-#endif
-
 #undef BITS32   // TODO
 #define BITS64  // TODO
 
-#if defined(WIN32)
+#ifdef _WIN32
 #define STDCALL __stdcall
 #if defined(IMPORT_EXPORTS)
 #define DLLEXPORT __declspec(dllimport)

c/flisp.c

@@ -2624,7 +2624,7 @@ static void lisp_init(size_t initial_heapsize)
 
 #ifdef LINUX
     set(symbol("*os-name*"), symbol("linux"));
-#elif defined(WIN32) || defined(WIN64)
+#elif defined(_WIN32)
     set(symbol("*os-name*"), symbol("win32"));
 #elif defined(MACOSX)
     set(symbol("*os-name*"), symbol("macos"));

c/ios.c

@@ -9,7 +9,7 @@
 
 #include "dtypes.h"
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <malloc.h>
 #include <io.h>
 #include <fcntl.h>
@@ -43,7 +43,7 @@ static void *our_memrchr(const void *s, int c, size_t n)
 // poll for read, unless forwrite!=0
 static void _fd_poll(long fd, int forwrite)
 {
-#ifndef WIN32
+#ifndef _WIN32
     fd_set set;
 
     FD_ZERO(&set);

c/socket.c

@@ -107,7 +107,7 @@ int open_any_udp_port(short *portno)
     return sockfd;
 }
 
-#ifndef WIN32
+#ifndef _WIN32
 void closesocket(int fd) { close(fd); }
 #endif
 

c/socket.h

@@ -1,4 +1,4 @@
-#ifdef WIN32
+#ifdef _WIN32
 #include <winsock2.h>
 #else
 #include <netinet/in.h>
@@ -8,6 +8,10 @@
 #include <fcntl.h>
 #endif
 
+#ifndef _WIN32
+void closesocket(int fd);
+#endif
+
 int open_tcp_port(short portno);
 int open_any_tcp_port(short *portno);
 int open_any_udp_port(short *portno);
@@ -17,7 +21,3 @@ int sendall(int sockfd, char *buffer, int bufLen, int flags);
 int readall(int sockfd, char *buffer, int bufLen, int flags);
 int addr_eq(struct sockaddr_in *a, struct sockaddr_in *b);
 int socket_ready(int sock);
-
-#ifndef WIN32
-void closesocket(int fd);
-#endif

c/utf8.c

@@ -23,7 +23,7 @@
 #include <wchar.h>
 #include <wctype.h>
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <malloc.h>
 #define snprintf _snprintf
 #endif
@@ -253,7 +253,7 @@ size_t u8_strlen(const char *s)
     return count;
 }
 
-#if defined(__WIN32__)
+#ifdef _WIN32
 #include "wcwidth.h"
 #endif
 

c/utf8.h

@@ -1,6 +1,6 @@
 extern int locale_is_utf8;
 
-#if defined(__WIN32__)
+#ifdef _WIN32
 extern int wcwidth(uint32_t);
 #endif