Burn default ASAN options into the built Ruby

* We always need use_sigaltstack=0 because Ruby registers sigaltstack
  handlers
* We also need to disable leak detection (unless RUBY_FREE_AT_EXIT is
  set - I might experiment later with automatically enabling leak
  detection if RUBY_FREE_AT_EXIT is set).

Burning it into the built ruby binary in this way avoids people needing
to remember to start their Ruby program with these flags all the time.

We also need a small fix in mkmf to make sure that test programs also
don't have leak detection enabled (this is never desirable)

[Bug #20256]

common.mk

@@ -9325,11 +9325,15 @@ localeinit.$(OBJEXT): {$(VPATH)}st.h
 localeinit.$(OBJEXT): {$(VPATH)}subst.h
 main.$(OBJEXT): $(hdrdir)/ruby.h
 main.$(OBJEXT): $(hdrdir)/ruby/ruby.h
+main.$(OBJEXT): $(top_srcdir)/internal/compilers.h
+main.$(OBJEXT): $(top_srcdir)/internal/sanitizers.h
+main.$(OBJEXT): $(top_srcdir)/internal/warnings.h
 main.$(OBJEXT): {$(VPATH)}assert.h
 main.$(OBJEXT): {$(VPATH)}backward.h
 main.$(OBJEXT): {$(VPATH)}backward/2/assume.h
 main.$(OBJEXT): {$(VPATH)}backward/2/attributes.h
 main.$(OBJEXT): {$(VPATH)}backward/2/bool.h
+main.$(OBJEXT): {$(VPATH)}backward/2/gcc_version_since.h
 main.$(OBJEXT): {$(VPATH)}backward/2/inttypes.h
 main.$(OBJEXT): {$(VPATH)}backward/2/limits.h
 main.$(OBJEXT): {$(VPATH)}backward/2/long_long.h

lib/mkmf.rb

@@ -399,6 +399,11 @@ MESSAGE
       env, *commands = commands if Hash === commands.first
       envs.merge!(env) if env
     end
+
+    # disable ASAN leak reporting - conftest programs almost always don't bother
+    # to free their memory.
+    envs['ASAN_OPTIONS'] = "detect_leaks=0" unless ENV.key?('ASAN_OPTIONS')
+
     return envs, expand[commands]
   end
 

main.c

@@ -20,6 +20,7 @@
 #undef RUBY_EXPORT
 #include "ruby.h"
 #include "vm_debug.h"
+#include "internal/sanitizers.h"
 #ifdef HAVE_LOCALE_H
 #include <locale.h>
 #endif
@@ -57,3 +58,12 @@ main(int argc, char **argv)
     ruby_sysinit(&argc, &argv);
     return rb_main(argc, argv);
 }
+
+#ifdef RUBY_ASAN_ENABLED
+/* Compile in the ASAN options Ruby needs, rather than relying on environment variables, so
+ * that even tests which fork ruby with a clean environment will run ASAN with the right
+ * settings */
+const char *__asan_default_options(void) {
+  return "use_sigaltstack=0:detect_leaks=0";
+}
+#endif