patch 8.2.5057: using gettimeofday() for timeout is very inefficient

Problem:    Using gettimeofday() for timeout is very inefficient.
Solution:   Set a platform dependent timer. (Paul Ollis, closes #10505)
diff --git a/src/testdir/test_syntax.vim b/src/testdir/test_syntax.vim
index be2f458..82d5cbb 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -527,6 +527,15 @@
   CheckFunction reltimefloat
   CheckFeature syntax
 
+  " So, it turns out the Windows 7 implements TimerQueue timers differently
+  " and they can expire *before* the requested time has elapsed. So allow for
+  " the timeout occurring after 80 ms (5 * 16 (the typical clock tick)).
+  if has("win32")
+    let min_timeout = 0.08
+  else
+    let min_timeout = 0.1
+  endif
+
   " This pattern takes a long time to match, it should timeout.
   new
   call setline(1, ['aaa', repeat('abc ', 1000), 'ccc'])
@@ -535,7 +544,7 @@
   syn match Error /\%#=1a*.*X\@<=b*/
   redraw
   let elapsed = reltimefloat(reltime(start))
-  call assert_true(elapsed > 0.1)
+  call assert_true(elapsed > min_timeout)
   call assert_true(elapsed < 1.0)
 
   " second time syntax HL is disabled
@@ -549,7 +558,7 @@
   exe "normal \<C-L>"
   redraw
   let elapsed = reltimefloat(reltime(start))
-  call assert_true(elapsed > 0.1)
+  call assert_true(elapsed > min_timeout)
   call assert_true(elapsed < 1.0)
 
   set redrawtime&
@@ -642,7 +651,7 @@
 	\ "\tNote: asdf",
 	\ '}',
 	\ ], 'Xtest.c')
- 
+
   " This makes the default for 'background' use "dark", check that the
   " response to t_RB corrects it to "light".
   let $COLORFGBG = '15;0'