kconfig: tests: check unneeded "is not set" with unmet dependency

Commit cb67ab2cd2 ("kconfig: do not write choice values when their
dependency becomes n") fixed a problem where "# CONFIG_... is not set"
for choice values are wrongly written into the .config file when they
are once visible, then become invisible later.

Add a test for this naive case.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>

scripts/kconfig/tests/no_write_if_dep_unmet/Kconfig

@@ -0,0 +1,14 @@
+config A
+	bool "A"
+
+choice
+	prompt "Choice ?"
+	depends on A
+
+config CHOICE_B
+	bool "Choice B"
+
+config CHOICE_C
+	bool "Choice C"
+
+endchoice