build-sys: simplify AF_VSOCK check

The current test checks more than AF_VSOCK availability, and doesn't
need to be that long.

Since its introduction in Linux in 2013, AF_VSOCK came with
linux/vm_sockets.h for sockaddr_vm, let's check that.

We could even go back to the initial configure-less approach
proposed by Stefan Hajnoczi, since Michael Roth added the configure-time
check back then to satisfy glibc in Ubuntu 14. See:
https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg08208.html

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220401115005.2204000-1-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -1988,25 +1988,10 @@ have_afalg = get_option('crypto_afalg') \
   '''), error_message: 'AF_ALG requested but could not be detected').allowed()
 config_host_data.set('CONFIG_AF_ALG', have_afalg)
 
-config_host_data.set('CONFIG_AF_VSOCK', cc.compiles(gnu_source_prefix + '''
-  #include <errno.h>
-  #include <sys/types.h>
-  #include <sys/socket.h>
-  #if !defined(AF_VSOCK)
-  # error missing AF_VSOCK flag
-  #endif
-  #include <linux/vm_sockets.h>
-  int main(void) {
-    int sock, ret;
-    struct sockaddr_vm svm;
-    socklen_t len = sizeof(svm);
-    sock = socket(AF_VSOCK, SOCK_STREAM, 0);
-    ret = getpeername(sock, (struct sockaddr *)&svm, &len);
-    if ((ret == -1) && (errno == ENOTCONN)) {
-        return 0;
-    }
-    return -1;
-  }'''))
+config_host_data.set('CONFIG_AF_VSOCK', cc.has_header_symbol(
+  'linux/vm_sockets.h', 'AF_VSOCK',
+  prefix: '#include <sys/socket.h>',
+))
 
 have_vss = false
 have_vss_sdk = false # old xp/2003 SDK