Mark some tests as big.

Setting these tests to use 3 processors is weird, but it means that in
CI (where we do 4 tests in parallel), we won't ever run more than one of
these at a time (though we can run any other one test at the same time
as these).  This should fix the intermittent failure.

Test/CMakeLists.txt

@@ -138,3 +138,12 @@ addtest_variants("ForwardDeclareProtocolAccess" "ForwardDeclareProtocolAccess.m;
 if (ENABLE_OBJCXX)
 	addtest_variants(ObjCXXEHInterop "ObjCXXEHInterop.mm;ObjCXXEHInterop.m" true)
 endif()
+
+# Some tests use enough memory that they fail on CI intermittently if they
+# happen to run in parallel with each other.
+set_tests_properties(ManyManySelectors PROPERTIES PROCESSORS 3)
+set_tests_properties(ManyManySelectors_optimised PROPERTIES PROCESSORS 3)
+if (${LEGACY})
+	set_tests_properties(ManyManySelectors_legacy PROPERTIES PROCESSORS 3)
+	set_tests_properties(ManyManySelectors_legacy_optimised PROPERTIES PROCESSORS 3)
+endif ()