gfxstream: Avoid repeated functionality

Removed a function that creates anonymous file descriptors when called.
Additionally replaced a call of said function with the one from the "util"
directory. The intention is to avoid repeated functionality

util: Allow code to be compatible in c++ compilers

Added an extern "C" statement and preprocessor directives to make the
“os_create_anonymous_file” function compatible with c++ compilers

Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32096>

src/util/anon_file.h

@@ -28,7 +28,15 @@
 
 #include <stdint.h>
 
+#ifdef __cplusplus
+extern "C"{
+#endif
+
 /* On win32, off_t is only 32 bit, so always using 64 bit size */
 int os_create_anonymous_file(int64_t size, const char *debug_name);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif