Guard the disabled tests with a macro rather than #if 0

Clang-Tidy's readability-avoid-unconditional-preprocessor-if rejects a literal
#if 0. Use a macro that is never defined instead, which the check does not
look at. Still temporary, and reverted together with the previous commit.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/unit-custom-array-type.cpp

@@ -19,8 +19,9 @@
 
 // TEMPORARY: this translation unit is disabled to narrow down an AppVeyor
 // failure on MSVC 2015/2017 whose build log this environment cannot reach.
-// The guard is removed again as soon as the cause is known.
-#if 0
+// The macro is deliberately never defined; the guard is removed again as soon
+// as the cause is known.
+#ifdef JSON_BISECT_CUSTOM_CONTAINER_TESTS
 
 namespace
 {

tests/src/unit-custom-binary-type.cpp

@@ -23,8 +23,9 @@
 
 // TEMPORARY: this translation unit is disabled to narrow down an AppVeyor
 // failure on MSVC 2015/2017 whose build log this environment cannot reach.
-// The guard is removed again as soon as the cause is known.
-#if 0
+// The macro is deliberately never defined; the guard is removed again as soon
+// as the cause is known.
+#ifdef JSON_BISECT_CUSTOM_CONTAINER_TESTS
 
 namespace
 {

tests/src/unit-custom-object-type.cpp

@@ -19,8 +19,9 @@
 
 // TEMPORARY: this translation unit is disabled to narrow down an AppVeyor
 // failure on MSVC 2015/2017 whose build log this environment cannot reach.
-// The guard is removed again as soon as the cause is known.
-#if 0
+// The macro is deliberately never defined; the guard is removed again as soon
+// as the cause is known.
+#ifdef JSON_BISECT_CUSTOM_CONTAINER_TESTS
 
 namespace
 {