riscv: Disable STACKPROTECTOR_PER_TASK if GCC_PLUGIN_RANDSTRUCT is enabled

riscv uses the value of TSK_STACK_CANARY to set
stack-protector-guard-offset. With GCC_PLUGIN_RANDSTRUCT enabled, that
value is non-deterministic, and with riscv:allmodconfig often results
in build errors such as

cc1: error: '8120' is not a valid offset in '-mstack-protector-guard-offset='

Enable STACKPROTECTOR_PER_TASK only if GCC_PLUGIN_RANDSTRUCT is disabled
to fix the problem.

Fixes: fea2fed2 ("riscv: Enable per-task stack canaries")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -492,6 +492,7 @@ config CC_HAVE_STACKPROTECTOR_TLS
 
 config STACKPROTECTOR_PER_TASK
 	def_bool y
+	depends on !GCC_PLUGIN_RANDSTRUCT
 	depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_TLS
 
 config PHYS_RAM_BASE