Fix the Watcom build, and UNC paths in httpsrv on Windows

Open Watcom has no struct _stat64 or _wstat64: its 64-bit stat is
struct _stati64 and _wstati64, so httpsrv.c did not compile there and
the 1.0.1 lite build had no binaries.

widepath() compared and wrote '\\\\', a two-character constant, for a
backslash: a UNC path (\\server\share) never took the \\?\UNC\ form,
and forward slashes became backslashes only because the constant was
truncated to its last byte.

The Watcom workflow passed although nmake failed; it now fails when
the build does or leaves no 3proxy.exe.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit 9651848bf1)

.github/workflows/build-watcom.yml

@@ -40,6 +40,8 @@ jobs:
       run: |
        echo "volatile char VerSion[]=^"3APA3A-3proxy-Internal-Build: 3proxy-%RELEASE%-%NOW%\r\n^";" >>src/3proxy.c
        nmake /F Makefile.watcom
+       if errorlevel 1 exit /b 1
+       if not exist bin\3proxy.exe (echo bin\3proxy.exe was not built & exit /b 1)
     - name: make dist dir
       shell: cmd
       run: |

src/httpsrv.c

@@ -457,12 +457,12 @@ static int widepath(const char *path, wchar_t *out, int outchars)
 	char *p;
 
 	if(!strncmp(path, "\\\\?\\", 4)) snprintf(prefixed, sizeof(prefixed), "%s", path);
-	else if(path[0] == '\\\\' && path[1] == '\\\\')
+	else if(path[0] == '\\' && path[1] == '\\')
 		snprintf(prefixed, sizeof(prefixed), "\\\\?\\UNC\\%s", path + 2);
 	else snprintf(prefixed, sizeof(prefixed), "\\\\?\\%s", path);
 
 	/* the extended form takes no forward slashes */
-	for(p = prefixed; *p; p++) if(*p == '/') *p = '\\\\';
+	for(p = prefixed; *p; p++) if(*p == '/') *p = '\\';
 
 	return MultiByteToWideChar(CP_UTF8, 0, prefixed, -1, out, outchars) > 0? 0 : 1;
 }
@@ -479,9 +479,19 @@ static int filemeta(const char *path, struct filemeta *m)
 {
 #ifdef _WIN32
 	wchar_t wide[HTTPSRV_LINE];
+#ifdef __WATCOMC__
+	/* Open Watcom has the 64-bit stat under its older name */
+#ifndef _S_IFREG
+#define _S_IFREG S_IFREG
+#endif
+	struct _stati64 st;
+
+	if(widepath(path, wide, HTTPSRV_LINE) || _wstati64(wide, &st)) return 1;
+#else
 	struct _stat64 st;
 
 	if(widepath(path, wide, HTTPSRV_LINE) || _wstat64(wide, &st)) return 1;
+#endif
 	m->size = (uint64_t)st.st_size;
 	m->mtime = st.st_mtime;
 	m->isreg = (st.st_mode & _S_IFREG) != 0;