gcc-plugins: Adjust Kconfig to avoid cyc_complexity

In preparation for removing "depends on !COMPILE_TEST" from GCC_PLUGINS,
the GCC_PLUGIN_CYC_COMPLEXITY plugin needs to gain the restriction,
since it is mainly an example, and produces (intended) voluminous stderr
reporting, which is generally undesirable for allyesconfig-style build
tests. This additionally puts the plugin behind EXPERT and improves the
help text.
Signed-off-by: Kees Cook <keescook@chromium.org>

arch/Kconfig

@@ -363,8 +363,9 @@ menuconfig GCC_PLUGINS
 	  See Documentation/gcc-plugins.txt for details.
 
 config GCC_PLUGIN_CYC_COMPLEXITY
-	bool "Compute the cyclomatic complexity of a function"
+	bool "Compute the cyclomatic complexity of a function" if EXPERT
 	depends on GCC_PLUGINS
+	depends on !COMPILE_TEST
 	help
 	  The complexity M of a function's control flow graph is defined as:
 	   M = E - N + 2P
@@ -374,6 +375,10 @@ config GCC_PLUGIN_CYC_COMPLEXITY
 	  N = the number of nodes
 	  P = the number of connected components (exit nodes).
 
+	  Enabling this plugin reports the complexity to stderr during the
+	  build. It mainly serves as a simple example of how to create a
+	  gcc plugin for the kernel.
+
 config GCC_PLUGIN_SANCOV
 	bool
 	depends on GCC_PLUGINS