[test] Skip some tests on gc fuzzer

NOTRY=true
TBR=majeski@google.com

Bug: v8:7012
Change-Id: Iaac782596ab3fdb7338f04fe7b3af7474b36fa57
Reviewed-on: https://chromium-review.googlesource.com/766347Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49329}

test/mjsunit/mjsunit.status

@@ -265,7 +265,8 @@
   'wasm/js-api': [SKIP],
 
   # BUG(chromium:773631): Crashes flakily.
-  'wasm/streaming-trap-location': [SKIP]
+  'wasm/streaming-trap-location': [SKIP],
+
 }],  # 'gc_stress == True'
 
 ##############################################################################
@@ -600,6 +601,13 @@
   'es6/array-iterator-turbo': [SKIP]
 }],  # 'deopt_fuzzer == True'
 
+##############################################################################
+['gc_fuzzer == True', {
+  'regress/regress-336820': [SKIP],
+  'regress/regress-748069': [SKIP],
+  'regress/regress-778668': [SKIP],
+}],  # 'gc_fuzzer == True'
+
 ##############################################################################
 ['predictable == True', {