osdep: build with non-working system() function

Build without error on hosts without a working system(). If system()
is called, return -1 with ENOSYS.

Signed-off-by: Joelle van Dyne <j@getutm.app>
Message-id: 20210126012457.39046-6-j@getutm.app
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/qemu/osdep.h

@@ -710,4 +710,16 @@ static inline void qemu_thread_jit_write(void) {}
 static inline void qemu_thread_jit_execute(void) {}
 #endif
 
+/**
+ * Platforms which do not support system() return ENOSYS
+ */
+#ifndef HAVE_SYSTEM_FUNCTION
+#define system platform_does_not_support_system
+static inline int platform_does_not_support_system(const char *command)
+{
+    errno = ENOSYS;
+    return -1;
+}
+#endif /* !HAVE_SYSTEM_FUNCTION */
+
 #endif

meson.build

@@ -1127,6 +1127,7 @@ config_host_data.set('HAVE_DRM_H', cc.has_header('libdrm/drm.h'))
 config_host_data.set('HAVE_PTY_H', cc.has_header('pty.h'))
 config_host_data.set('HAVE_SYS_IOCCOM_H', cc.has_header('sys/ioccom.h'))
 config_host_data.set('HAVE_SYS_KCOV_H', cc.has_header('sys/kcov.h'))
+config_host_data.set('HAVE_SYSTEM_FUNCTION', cc.has_function('system', prefix: '#include <stdlib.h>'))
 
 config_host_data.set('CONFIG_PREADV', cc.has_function('preadv', prefix: '#include <sys/uio.h>'))