tests/tcg: Replace -mpower8-vector with -mcpu=power8

[1] deprecated -mpower8-vector, resulting in:

    powerpc64-linux-gnu-gcc: warning: switch '-mpower8-vector' is no longer supported
    qemu/tests/tcg/ppc64/vsx_f2i_nan.c:4:15: error: expected ';' before 'float'
        4 | typedef vector float vsx_float32_vec_t;
          |               ^~~~~~

Use -mcpu=power8 instead. In order to properly verify that this works,
one needs a big-endian (the minimum supported CPU for 64-bit
little-endian is power8 anyway) GCC configured with --enable-checking
(see GCC commit e154242724b0 ("[RS6000] Don't pass -many to the
assembler").

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109987

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20241023131250.48510-1-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tests/tcg/ppc64/Makefile.target

@@ -6,7 +6,7 @@ VPATH += $(SRC_PATH)/tests/tcg/ppc64
 
 config-cc.mak: Makefile
 	$(quiet-@)( \
-	    $(call cc-option,-mpower8-vector,   CROSS_CC_HAS_POWER8_VECTOR); \
+	    $(call cc-option,-mcpu=power8,      CROSS_CC_HAS_CPU_POWER8); \
 	    $(call cc-option,-mpower10,         CROSS_CC_HAS_POWER10)) 3> config-cc.mak
 
 -include config-cc.mak
@@ -23,15 +23,15 @@ run-threadcount: threadcount
 run-plugin-threadcount-with-%:
 	$(call skip-test, $<, "BROKEN (flaky with clang) ")
 
-ifneq ($(CROSS_CC_HAS_POWER8_VECTOR),)
+ifneq ($(CROSS_CC_HAS_CPU_POWER8),)
 PPC64_TESTS=bcdsub non_signalling_xscv
 endif
-$(PPC64_TESTS): CFLAGS += -mpower8-vector
+$(PPC64_TESTS): CFLAGS += -mcpu=power8
 
-ifneq ($(CROSS_CC_HAS_POWER8_VECTOR),)
+ifneq ($(CROSS_CC_HAS_CPU_POWER8),)
 PPC64_TESTS += vsx_f2i_nan
 endif
-vsx_f2i_nan: CFLAGS += -mpower8-vector -I$(SRC_PATH)/include
+vsx_f2i_nan: CFLAGS += -mcpu=power8 -I$(SRC_PATH)/include
 
 PPC64_TESTS += mtfsf
 PPC64_TESTS += mffsce