Disable signal handling of JVM GC signals

The JVM uses signals as an efficient way to do GC safe-pointing. When
clang is loaded as a native library on the JVM, the LLVM signal handler
ends up getting triggered by the signals generated by the GC mechanism.
This problem is addressed by libjsig, but that approach requires
preloading the library on JVM startup, which cannot be ensured when
using Gradle daemons. Furthermore, libjsig does not work on newer
versions of MacOS.

llvm/lib/Support/Unix/Signals.inc

@@ -297,6 +297,17 @@ static void RegisterHandlers() { // Not signal-safe.
 
   enum class SignalKind { IsKill, IsInfo };
   auto registerHandler = [&](int Signal, SignalKind Kind) {
+    /// KOTLIN/NATIVE SPECIFIC HACK
+    ///
+    /// We need to disable handling of signals that can originate from the JVM GC,
+    /// since they should not trigger the LLVM signal handler.
+
+    static const int JvmSigs[] = {
+      SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGUSR1, SIGUSR2
+    };
+
+    for (auto S : JvmSigs) if (Signal == S) return;
+
     unsigned Index = NumRegisteredSignals.load();
     assert(Index < array_lengthof(RegisteredSignalInfo) &&
            "Out of space for signal handlers!");