Fix detected leaks/heap-use-after-free by AddressSanitizer at startup

(cherry picked from commit 3f94ea62716ca9360b470a1711d58631021ccaed)

platform/x11/detect_prime.cpp

@@ -175,7 +175,7 @@ int detect_prime() {
 			close(fdset[0]);
 
 		} else {
-			// In child, exit() here will not quit the engine.
+			// In child, killing this process will not quit the engine.
 
 			char string[201];
 
@@ -203,7 +203,7 @@ int detect_prime() {
 				print_verbose("Couldn't write vendor/renderer string.");
 			}
 			close(fdset[1]);
-			exit(0);
+			raise(SIGINT);
 		}
 	}