fixes #19713; Revert "Remove tlsEmulation enabled from Windows + GCC config" (#19119) (#20327)

* Revert "Remove tlsEmulation enabled from Windows + GCC config (#19119) [backport:1.6]"

This reverts commit 77b696c2c9.

* increase nimTlsSize to 48000

* enable for windows

* fixes tests

* fixes tlsEmulation:on

compiler/nim.cfg

@@ -11,6 +11,7 @@ define:nimPreviewSlimSystem
 
 @if windows:
   cincludes: "$lib/wrappers/libffi/common"
+  tlsEmulation:off
 @end
 
 define:useStdoutAsStdmsg

compiler/ropes.nim

@@ -86,8 +86,12 @@ proc newRope(data: string = ""): Rope =
   result.L = -data.len
   result.data = data
 
-var
-  cache {.threadvar.} : array[0..2048*2 - 1, Rope]
+when compileOption("tlsEmulation"): # fixme: be careful if you want to make ropes support multiple threads
+  var
+    cache: array[0..2048*2 - 1, Rope]
+else:
+  var
+    cache {.threadvar.} : array[0..2048*2 - 1, Rope]
 
 proc resetRopeCache* =
   for i in low(cache)..high(cache):