Fix = vs == typos in test assertions. NFC

I first noticed a type in audioworklet_params_mixing.c from emscripten-core#23659 then
found several other tests with the same issue.  Nasty.

Not sure what to do about the test_sdl_set_clip_rect assertions which
don't seem to be valid (i.e. they fail with the typo fixed).

Author: sbc100

test/core/test_dlfcn_self.c

@@ -22,7 +22,7 @@ void repeatable() {
 
   int* global_ptr = (int*)dlsym(self, "global");
   assert(global_ptr);
-  assert(*global_ptr = 123);
+  assert(*global_ptr == 123);
 
   void (*foo_ptr)(int) = (void (*)(int))dlsym(self, "foo");
   assert(foo_ptr);

test/other/test_stat_fail_alongtheway.c

@@ -14,7 +14,7 @@ int main() {
   {
     struct stat st;
     assert(stat("path", &st) == 0);
-    assert(st.st_mode = 0777);
+    assert((st.st_mode & ~S_IFMT) == 0777);
   }
   {
     struct stat st;
@@ -25,7 +25,7 @@ int main() {
   {
     struct stat st;
     assert(stat("path/file", &st) == 0);
-    assert(st.st_mode = 0666);
+    assert((st.st_mode & ~S_IFMT) == 0644);
   }
   {
     struct stat st;

test/unistd/truncate.c

@@ -19,13 +19,13 @@ void setup() {
   FILE* f = fopen("towrite", "w");
   assert(f);
   rtn = fwrite("abcdef", 6, 1, f);
-  assert(rtn = 6);
+  assert(rtn == 1);
   fclose(f);
 
   f = fopen("toread", "w");
   assert(f);
   rtn = fwrite("abcdef", 6, 1, f);
-  assert(rtn = 6);
+  assert(rtn == 1);
   fclose(f);
 
   assert(chmod("toread", 0444) == 0);

test/webaudio/audioworklet_params_mixing.c

@@ -33,7 +33,7 @@ bool process(int numInputs, const AudioSampleFrame* inputs, int numOutputs, Audi
   // Interestingly, params varies per browser. Chrome won't have a length > 1
   // unless the value changes, and FF has all 128 entries even for a k-rate
   // parameter. The only given is that two params are incoming:
-  assert(numParams = 2);
+  assert(numParams == 2);
   assert(params[0].length == 1 || params[0].length == outSamplesPerChannel);
   assert(params[1].length == 1 || params[1].length == outSamplesPerChannel);
   // We can now do a quick mix since we know the layouts