arch_init: Fix AltiVec build on Darwin/ppc

Commit f29a56147b (implement
-no-user-config command-line option (v3)) introduced uses of bool
in arch_init.c. Shortly before that usage is support code for
AltiVec (conditional to __ALTIVEC__).

GCC's altivec.h may in a !__APPLE_ALTIVEC__ code path redefine bool,
leading to type mismatches. altivec.h recommends to #undef for C++
compatibility, but doing so in C leads to bool remaining undefined.

Fix by redefining bool to _Bool as mandated for stdbool.h by POSIX.

Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

arch_init.c

@@ -100,6 +100,10 @@ const uint32_t arch_type = QEMU_ARCH;
 #define VECTYPE        vector unsigned char
 #define SPLAT(p)       vec_splat(vec_ld(0, p), 0)
 #define ALL_EQ(v1, v2) vec_all_eq(v1, v2)
+/* altivec.h may redefine the bool macro as vector type.
+ * Reset it to POSIX semantics. */
+#undef bool
+#define bool _Bool
 #elif defined __SSE2__
 #include <emmintrin.h>
 #define VECTYPE        __m128i