lttng-tools: Disable on qemuriscv32

lttng-tools requires SYS_ppoll and SYS_pselect6 which are not supported on
riscv32. This has been confirmed by lttng-tools upstream.
lttng/lttng-tools#162

It's also turned off for riscv32 in meta-riscv.
https://github.com/riscv/meta-riscv/blob/master/conf/layer.conf

Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 68b07bb)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/recipes-kernel/lttng/lttng-platforms.inc

@@ -15,3 +15,7 @@ LTTNGUST:arc = ""
 
 COMPATIBLE_HOST:arc:pn-lttng-ust = "null"
 
+# Whether the platform supports lttng-tools
+# lttng-tools requires SYS_ppoll and SYS_pselect6 which are not supported on riscv32.
+# It's also turned off for riscv32 in meta-riscv. See https://github.com/riscv/meta-riscv/blob/master/conf/layer.conf
+COMPATIBLE_HOST:qemuriscv32:pn-lttng-tools = "null"