Handle SIGINT in the FuzzTest framework.

It was previous handled by the engine library. Now that the signal handler is no longer in the engine, the framework can handle the signal consistently.

PiperOrigin-RevId: 940538413

fuzztest/internal/centipede_adaptor.cc

diff --git a/fuzztest/internal/centipede_adaptor.cc b/fuzztest/internal/centipede_adaptor.cc
index 16b46cc..7c23407 100644
--- a/fuzztest/internal/centipede_adaptor.cc
+++ b/fuzztest/internal/centipede_adaptor.cc
@@ -355,7 +355,7 @@
 
 void InstallCentipedeTerminationHandler() {
   [[maybe_unused]] static bool install_once = [] {
-    for (int signum : {SIGTERM, SIGHUP}) {
+    for (int signum : {SIGTERM, SIGHUP, SIGINT}) {
       struct sigaction new_sigact = {};
       sigemptyset(&new_sigact.sa_mask);
       new_sigact.sa_handler = [](int signum) {
@@ -364,16 +364,22 @@
         const int fd =
             GetStderrFdDup() != -1 ? GetStderrFdDup() : STDERR_FILENO;
         if (signum == SIGTERM) {
-          constexpr char msg[] = "\n[!] SIGTERM received - stopping fuzzing.\n";
-          write(fd, msg, sizeof(msg) - 1);
+          constexpr char kMsg[] =
+              "\n[!] SIGTERM received - stopping fuzzing.\n";
+          write(fd, kMsg, sizeof(kMsg) - 1);
           return;
         } else if (signum == SIGHUP) {
-          constexpr char msg[] = "\n[!] SIGHUP received - stopping fuzzing.\n";
-          write(fd, msg, sizeof(msg) - 1);
+          constexpr char kMsg[] = "\n[!] SIGHUP received - stopping fuzzing.\n";
+          write(fd, kMsg, sizeof(kMsg) - 1);
+          return;
+        } else if (signum == SIGINT) {
+          constexpr char kMsg[] = "\n[!] SIGINT received - stopping fuzzing.\n";
+          write(fd, kMsg, sizeof(kMsg) - 1);
           return;
         }
-        constexpr char msg[] = "\n[!] Unexpected signal received - aborting.\n";
-        write(fd, msg, sizeof(msg) - 1);
+        constexpr char kMsg[] =
+            "\n[!] Unexpected signal received - aborting.\n";
+        write(fd, kMsg, sizeof(kMsg) - 1);
         std::abort();
       };