qemu/bswap: Use compiler __builtin_bswap() on NetBSD

Since commit efc6c070 ("configure: Add a test for the minimum
compiler version") the minimum compiler version required for GCC
is 4.8, which supports __builtin_bswap().
Remove the NetBSD specific ifdef'ry.

This reverts commit 1360677c
("makes NetBSD use the native bswap functions").

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230111163147.71761-7-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

include/qemu/bswap.h

 #ifndef BSWAP_H
 #define BSWAP_H
 
-#ifdef CONFIG_MACHINE_BSWAP_H
-# include <sys/endian.h>
-# include <machine/bswap.h>
-# else
-#define BSWAP_FROM_FALLBACKS
-#endif /* ! CONFIG_MACHINE_BSWAP_H */
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#ifdef BSWAP_FROM_FALLBACKS
 #undef  bswap16
 #define bswap16(_x) __builtin_bswap16(_x)
 #undef  bswap32
 #define bswap32(_x) __builtin_bswap32(_x)
 #undef  bswap64
 #define bswap64(_x) __builtin_bswap64(_x)
-#endif
-
-#undef BSWAP_FROM_FALLBACKS
 
 static inline void bswap16s(uint16_t *s)
 {

meson.build

@@ -2030,10 +2030,6 @@ config_host_data.set('CONFIG_INOTIFY',
                      cc.has_header_symbol('sys/inotify.h', 'inotify_init'))
 config_host_data.set('CONFIG_INOTIFY1',
                      cc.has_header_symbol('sys/inotify.h', 'inotify_init1'))
-config_host_data.set('CONFIG_MACHINE_BSWAP_H',
-                     cc.has_header_symbol('machine/bswap.h', 'bswap32',
-                                          prefix: '''#include <sys/endian.h>
-                                                     #include <sys/types.h>'''))
 config_host_data.set('CONFIG_PRCTL_PR_SET_TIMERSLACK',
                      cc.has_header_symbol('sys/prctl.h', 'PR_SET_TIMERSLACK'))
 config_host_data.set('CONFIG_RTNETLINK',