Use debug version of malloc when ASSERTIONS=1. NFC

Previously we were only using it with `ASSERTIONS=2`.  The debug version
dlmalloc has a lot very useful checks.  Enabling this found a few real
issues in our test code.

embuilder.py

@@ -63,6 +63,7 @@
     'libemmalloc-memvalidate-verbose',
     'libmimalloc',
     'libmimalloc-mt',
+    'libmimalloc-mt-debug',
     'libGL',
     'libGL-getprocaddr',
     'libGL-emu-getprocaddr',
@@ -101,6 +102,7 @@
     'libc++-mt',
     'libc++-mt-noexcept',
     'libdlmalloc-mt',
+    'libdlmalloc-mt-debug',
     'libGL-emu',
     'libGL-emu-webgl2-getprocaddr',
     'libGL-mt-getprocaddr',

test/other/test_tsearch.c

@@ -39,6 +39,10 @@ static void action(const void *nodep, VISIT which, int depth) {
     }
 }
 
+static void free_node(void* nodep) {
+    // no-op since we didn't allocate any per-node data
+}
+
 int main(void) {
     int  ptr[12];
     void *val = NULL;
@@ -51,6 +55,6 @@ int main(void) {
         assert(val);
     }
     twalk(root, action);
-    tdestroy(root, free);
+    tdestroy(root, free_node);
     return 0;
-} 
+}

test/test_other.py

@@ -7951,10 +7951,10 @@ def test_dlmalloc_modes(self):
         printf("double-freed\n");
       }
     ''')
-    self.run_process([EMCC, 'src.c'])
+    self.run_process([EMCC, 'src.c', '-O2'])
     self.assertContained('double-freed', self.run_js('a.out.js'))
     # in debug mode, the double-free is caught
-    self.run_process([EMCC, 'src.c', '-sASSERTIONS=2'])
+    self.run_process([EMCC, 'src.c', '-O0'])
     out = self.run_js('a.out.js', assert_returncode=NON_ZERO)
     self.assertContained('native code called abort()', out)
 
@@ -13384,7 +13384,7 @@ def test_standard_library_mapping(self):
 
     # Check that the linker was run with `-mt` variants because `-pthread` was passed.
     self.assertContained(' -lc-mt-debug ', err)
-    self.assertContained(' -ldlmalloc-mt ', err)
+    self.assertContained(' -ldlmalloc-mt-debug ', err)
     self.assertContained(' -lcompiler_rt-mt ', err)
 
   def test_explicit_gl_linking(self):

tools/system_libs.py

@@ -1766,7 +1766,7 @@ def vary_on(cls):
   def get_default_variation(cls, **kwargs):
     return super().get_default_variation(
       malloc=settings.MALLOC,
-      is_debug=settings.ASSERTIONS >= 2,
+      is_debug=settings.ASSERTIONS,
       is_tracing=settings.EMSCRIPTEN_TRACING,
       memvalidate='memvalidate' in settings.MALLOC,
       verbose='verbose' in settings.MALLOC,