enable segfault stack traces in stage1 compiler

src-self-hosted/stage1.zig

@@ -455,3 +455,10 @@ export const stage2_DepNextResult = extern struct {
         prereq,
     };
 };
+
+// ABI warning
+export fn stage2_attach_segfault_handler() void {
+    if (std.debug.runtime_safety and std.debug.have_segfault_handling_support) {
+        std.debug.attachSegfaultHandler();
+    }
+}

src/main.cpp

@@ -262,6 +262,8 @@ static bool get_cache_opt(CacheOpt opt, bool default_value) {
 extern "C" int ZigClang_main(int argc, char **argv);
 
 int main(int argc, char **argv) {
+    stage2_attach_segfault_handler();
+
     char *arg0 = argv[0];
     Error err;
 

src/userland.cpp

@@ -26,6 +26,8 @@ void stage2_zen(const char **ptr, size_t *len) {
     stage2_panic(msg, strlen(msg));
 }
 
+void stage2_attach_segfault_handler(void) { }
+
 void stage2_panic(const char *ptr, size_t len) {
     fwrite(ptr, 1, len, stderr);
     fprintf(stderr, "\n");

src/userland.h

@@ -113,6 +113,9 @@ ZIG_EXTERN_C void stage2_render_ast(struct Stage2Ast *ast, FILE *output_file);
 // ABI warning
 ZIG_EXTERN_C void stage2_zen(const char **ptr, size_t *len);
 
+// ABI warning
+ZIG_EXTERN_C void stage2_attach_segfault_handler(void);
+
 // ABI warning
 ZIG_EXTERN_C ZIG_ATTRIBUTE_NORETURN void stage2_panic(const char *ptr, size_t len);