fixes to allow the usage of clang on windows with the msvc abi and ms headers (#6442)

lib/pure/times.nim

@@ -83,16 +83,11 @@ when defined(posix) and not defined(JS):
 elif defined(windows):
   import winlean
 
-  when defined(vcc) or defined(bcc) or defined(icl):
   # newest version of Visual C++ defines time_t to be of 64 bits
   type TimeImpl {.importc: "time_t", header: "<time.h>".} = int64
   # visual c's c runtime exposes these under a different name
   var
     timezone {.importc: "_timezone", header: "<time.h>".}: int
-  else:
-    type TimeImpl {.importc: "time_t", header: "<time.h>".} = int
-    var
-      timezone {.importc, header: "<time.h>".}: int
 
   type
     Time* = distinct TimeImpl

lib/system.nim

@@ -2872,7 +2872,7 @@ when not defined(JS): #and not defined(nimscript):
         importc: when defined(bcc): "setmode" else: "_setmode",
         header: "<io.h>".}
       var
-        O_BINARY {.importc: "O_BINARY", nodecl.}: cint
+        O_BINARY {.importc: "_O_BINARY", header:"<fcntl.h>".}: cint
 
       # we use binary mode on Windows:
       c_setmode(c_fileno(stdin), O_BINARY)

lib/system/ansi_c.nim

@@ -103,7 +103,11 @@ proc c_sprintf(buf, frmt: cstring): cint {.
   importc: "sprintf", header: "<stdio.h>", varargs, noSideEffect.}
   # we use it only in a way that cannot lead to security issues
 
-proc c_fileno(f: File): cint {.
+when defined(windows):
+  proc c_fileno(f: File): cint {.
+      importc: "_fileno", header: "<stdio.h>".}
+else:
+  proc c_fileno(f: File): cint {.
       importc: "fileno", header: "<fcntl.h>".}
 
 proc c_malloc(size: csize): pointer {.

lib/system/sysio.nim

@@ -15,8 +15,11 @@
 {.push debugger:off .} # the user does not want to trace a part
                        # of the standard library!
 
-
+when defined(windows):
-proc c_fdopen(filehandle: cint, mode: cstring): File {.
+  proc c_fdopen(filehandle: cint, mode: cstring): File {.
+    importc: "_fdopen", header: "<stdio.h>".}
+else:
+  proc c_fdopen(filehandle: cint, mode: cstring): File {.
     importc: "fdopen", header: "<stdio.h>".}
 proc c_fputs(c: cstring, f: File): cint {.
   importc: "fputs", header: "<stdio.h>", tags: [WriteIOEffect].}

lib/windows/winlean.nim

@@ -14,8 +14,8 @@
 
 import dynlib
 
-when defined(vcc):
+
-  {.passC: "-DWIN32_LEAN_AND_MEAN".}
+{.passC: "-DWIN32_LEAN_AND_MEAN".}
 
 const
   useWinUnicode* = not defined(useWinAnsi)