Fix gc tests for BoehmGC (#7094)

tests/gc/gcleak.nim

@@ -13,11 +13,10 @@ proc MakeObj(): TTestObj =
   result.x = "Hello"
 
 for i in 1 .. 1_000_000:
-  when defined(gcMarkAndSweep):
+  when defined(gcMarkAndSweep) or defined(boehmgc):
     GC_fullcollect()
   var obj = MakeObj()
   if getOccupiedMem() > 300_000: quit("still a leak!")
 #  echo GC_getstatistics()
 
 echo "no leak: ", getOccupiedMem()
-

tests/gc/gcleak2.nim

@@ -16,7 +16,7 @@ proc MakeObj(): TTestObj =
 
 proc inProc() =
   for i in 1 .. 1_000_000:
-    when defined(gcMarkAndSweep):
+    when defined(gcMarkAndSweep) or defined(boehmgc):
       GC_fullcollect()
     var obj: TTestObj
     obj = MakeObj()
@@ -24,5 +24,3 @@ proc inProc() =
 
 inProc()
 echo "no leak: ", getOccupiedMem()
-
-

tests/gc/gcleak4.nim

@@ -38,7 +38,7 @@ proc newPlus(a, b: ref TExpr): ref TPlusExpr =
   result.b = b
   result.op2 = $getOccupiedMem()
 
-const Limit = when compileOption("gc", "markAndSweep"): 5*1024*1024 else: 500_000
+const Limit = when compileOption("gc", "markAndSweep") or compileOption("gc", "boehm"): 5*1024*1024 else: 500_000
 
 for i in 0..100_000:
   var s: array[0..11, ref TExpr]