Expose install_fatal_error_handler() through the C API.

I expose the API with some caveats:

- The C++ API involves a traditional void* opaque pointer for the fatal 
error callback.  The C API doesn’t do this.  I don’t think that the void* 
opaque pointer makes any sense since this is a global callback - there will 
only be one of them.  So if you need to pass some data to your callback, 
just put it in a global variable.

- The bindings will ignore the gen_crash_diag boolean.  I ignore it because 
(1) I don’t know what it does, (2) it’s not documented AFAIK, and (3) I 
couldn’t imagine any use for it.  I made the gut call that it probably 
wasn’t important enough to expose through the C API.

llvm-svn: 192864

include/llvm-c/Core.h

@@ -416,6 +416,22 @@ void LLVMShutdown();
 char *LLVMCreateMessage(const char *Message);
 void LLVMDisposeMessage(char *Message);
 
+typedef void (*LLVMFatalErrorHandler)(const char *Reason);
+
+/**
+ * Install a fatal error handler. By default, if LLVM detects a fatal error, it
+ * will call exit(1). This may not be appropriate in many contexts. For example,
+ * doing exit(1) will bypass many crash reporting/tracing system tools. This
+ * function allows you to install a callback that will be invoked prior to the
+ * call to exit(1).
+ */
+void LLVMInstallFatalErrorHandler(LLVMFatalErrorHandler Handler);
+
+/**
+ * Reset the fatal error handler. This resets LLVM's fatal error handling
+ * behavior to the default.
+ */
+void LLVMResetFatalErrorHandler(void);
 
 /**
  * @defgroup LLVMCCoreContext Contexts

lib/Support/ErrorHandling.cpp

@@ -20,6 +20,7 @@
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm-c/Core.h"
 #include <cassert>
 #include <cstdlib>
 
@@ -102,3 +103,19 @@ void llvm::llvm_unreachable_internal(const char *msg, const char *file,
   LLVM_BUILTIN_UNREACHABLE;
 #endif
 }
+
+static void bindingsErrorHandler(void *user_data, const std::string& reason,
+                                 bool gen_crash_diag) {
+  LLVMFatalErrorHandler handler =
+    reinterpret_cast<LLVMFatalErrorHandler>(user_data);
+  handler(reason.c_str());
+}
+
+void LLVMInstallFatalErrorHandler(LLVMFatalErrorHandler Handler) {
+  install_fatal_error_handler(
+    bindingsErrorHandler, reinterpret_cast<void*>(Handler));
+}
+
+void LLVMResetFatalErrorHandler() {
+  remove_fatal_error_handler();
+}