riscv: Select HAVE_DYNAMIC_FTRACE when -fpatchable-function-entry is available

clang prior to 13.0.0 does not support -fpatchable-function-entry for
RISC-V.

clang: error: unsupported option '-fpatchable-function-entry=8' for target 'riscv64-unknown-linux-gnu'

To avoid this error, only select HAVE_DYNAMIC_FTRACE when this option is
not available.

Fixes: afc76b8 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
Link: ClangBuiltLinux#1268
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Reviewed-by: Fangrui Song <[email protected]>
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: nathanchance

arch/riscv/Kconfig

@@ -231,7 +231,7 @@ config ARCH_RV64I
 	bool "RV64I"
 	select 64BIT
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && GCC_VERSION >= 50000
-	select HAVE_DYNAMIC_FTRACE if MMU
+	select HAVE_DYNAMIC_FTRACE if MMU && $(cc-option,-fpatchable-function-entry=8)
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_GRAPH_TRACER