disable some tests for the C++ target; refs #7870

tests/coroutines/texceptions.nim

@@ -1,3 +1,7 @@
+discard """
+  target: "c"
+"""
+
 import coro
 var
   stackCheckValue = 1100220033

tests/coroutines/tgc.nim

@@ -1,3 +1,7 @@
+discard """
+  target: "c"
+"""
+
 import coro
 
 var maxOccupiedMemory = 0

tests/coroutines/titerators.nim

@@ -1,3 +1,7 @@
+discard """
+  target: "c"
+"""
+
 import coro
 include system/timers
 

tests/coroutines/twait.nim

@@ -1,6 +1,7 @@
 discard """
   output: "Exit 1\nExit 2"
   disabled: "macosx"
+  target: "c"
 """
 import coro