gcc-plugins: allow to enable GCC_PLUGINS for COMPILE_TEST

Now that the compiler's plugin support is checked in Kconfig,
all{yes,mod}config will not be bothered.

Remove 'depends on !COMPILE_TEST' for GCC_PLUGINS.

'depends on !COMPILE_TEST' for the following three are still kept:
GCC_PLUGIN_CYC_COMPLEXITY
GCC_PLUGIN_STRUCTLEAK_VERBOSE
GCC_PLUGIN_RANDSTRUCT_PERFORMANCE

Kees suggested to do so because the first two are too noisy, and the
last one would reduce the compile test coverage. I commented the
reasons in arch/Kconfig.

Signed-off-by: Masahiro Yamada <[e-mail]>
Acked-by: Kees Cook <[e-mail]>

arch/Kconfig

···
 	bool "GCC plugins"
 	depends on HAVE_GCC_PLUGINS
 	depends on PLUGIN_HOSTCC != ""
-	depends on !COMPILE_TEST
 	help
 	  GCC plugins are loadable modules that provide extra features to the
 	  compiler. They are useful for runtime instrumentation and static analysis.
···
 config GCC_PLUGIN_CYC_COMPLEXITY
 	bool "Compute the cyclomatic complexity of a function" if EXPERT
 	depends on GCC_PLUGINS
-	depends on !COMPILE_TEST
+	depends on !COMPILE_TEST	# too noisy
 	help
 	  The complexity M of a function's control flow graph is defined as:
 	   M = E - N + 2P
···
 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 	bool "Report forcefully initialized variables"
 	depends on GCC_PLUGIN_STRUCTLEAK
-	depends on !COMPILE_TEST
+	depends on !COMPILE_TEST	# too noisy
 	help
 	  This option will cause a warning to be printed each time the
 	  structleak plugin finds a variable it thinks needs to be
···
 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 	bool "Use cacheline-aware structure randomization"
 	depends on GCC_PLUGIN_RANDSTRUCT
-	depends on !COMPILE_TEST
+	depends on !COMPILE_TEST	# do not reduce test coverage
 	help
 	  If you say Y here, the RANDSTRUCT randomization will make a
 	  best effort at restricting randomization to cacheline-sized