tests/tcg/ppc64le: Fix compile flags for byte_reverse

With a host compiler new enough to recognize power10 insns,
CROSS_CC_HAS_POWER10 is true, but we do not supply the -cpu
option to the compiler, resulting in

/tmp/ccAVdYJd.s: Assembler messages:
/tmp/ccAVdYJd.s:49: Error: unrecognized opcode: `brh'
/tmp/ccAVdYJd.s:78: Error: unrecognized opcode: `brw'
/tmp/ccAVdYJd.s:107: Error: unrecognized opcode: `brd'
make[2]: *** [byte_reverse] Error 1

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

tests/tcg/ppc64le/Makefile.target

@@ -9,18 +9,12 @@ PPC64LE_TESTS=bcdsub
 endif
 bcdsub: CFLAGS += -mpower8-vector
 
-PPC64LE_TESTS += byte_reverse
 ifneq ($(DOCKER_IMAGE)$(CROSS_CC_HAS_POWER10),)
+PPC64LE_TESTS += byte_reverse
+endif
+byte_reverse: CFLAGS += -mcpu=power10
 run-byte_reverse: QEMU_OPTS+=-cpu POWER10
 run-plugin-byte_reverse-with-%: QEMU_OPTS+=-cpu POWER10
-else
-byte_reverse:
-	$(call skip-test, "BUILD of $@", "missing compiler support")
-run-byte_reverse:
-	$(call skip-test, "RUN of byte_reverse", "not built")
-run-plugin-byte_reverse-with-%:
-	$(call skip-test, "RUN of byte_reverse ($*)", "not built")
-endif
 
 PPC64LE_TESTS += signal_save_restore_xer